Is it permissible for him to ask Allaah for the girl who died and to whom he wanted to propose marriage to let her be his bride in Paradise?
Question

                The daughter of my maternal uncle died in an accident, and I was intending to propose marriage to her. Is it permissible to pray to Allaah to make her my bride in Paradise, or is this overstepping the mark in du’aa’? May Allaah reward you with good.
Praise be to Allah.First of all, we ask Allaah 
    to encompass that girl with His mercy, and to admit her to His Paradise, and 
    to bless her family and all her relatives with patience and consolation. 
We advise you to treat her 
    parents kindly, and help them to overcome their trial. With regard to 
    yourself, we advise you to accept the decree of Allaah and to have faith 
    that all things are in His hand (?), and that He controls all things in this 
    universe, and He has great wisdom and He cannot questioned as to what He 
    does, while they will be questioned. 
With regard to your 
    question about praying that this girl will be your wife in Paradise, there 
    is no reason why you should not do that, if Allaah wills, and you may pray 
    for that. 
But what we would prefer 
    for you is to pray to Allaah for mercy and forgiveness, and to raise her in 
    status in Paradise. This is what will benefit her from you, and you will be 
    rewarded for it, if Allaah Wills. 
We are afraid that you may 
    exaggerate about this matter, or use this du’aa’ too much, and that it may 
    increase your attachment to her and affects your life or distract you from 
    seeking that which will keep you chaste in this world, namely halaal 
    marriage. We should also point out to you, so that you will not go to 
    extremes in your attachment to her, that she has died and is a non-mahram to 
    you, so be aware of going to extremes in expressing grief and sorrow for 
    what you have missed out on, for Allaah has set an appointed time for all 
    things. 
We remind you of the verses 
    in which Allaah says (interpretation of the meaning): 
“And certainly, We shall 
    test you with something of fear, hunger, loss of wealth, lives and fruits, 
    but give glad tidings to As‑ Saabiroon (the patient). 
156. Who, when afflicted 
    with calamity, say: ‘Truly, to Allaah we belong and truly, to Him we shall 
    return.’
157. They are those on 
    whom are the Salawaat (i.e. who are blessed and will be forgiven) from their 
    Lord, and (they are those who) receive His Mercy, and it is they who are the 
    guided ones”
[al-Baqarah 2:155-157]
Shaykh al-Sa’di (may Allaah 
    have mercy on him) said: 
Allaah tells us that He 
    will inevitably test His slaves with trials, so as to differentiate those 
    who are sincere from those who are lying, those who panic from those who 
    have patience. This is His way with His slaves, because if ease were to 
    continue with those who believe and no trials were to befall them, there 
    would be no distinction between those who have faith and those who do not, 
    which leads to corruption. The wisdom of Allaah dictates that the people of 
    good should be differentiated from the people of evil. 
This is the purpose of 
    trials, not to take away what the believers have of faith or to turn them 
    away from their religion. Allaah never causes the faith of the believers to 
    be lost, and He tells us in this verse that He will test His slaves “with 
    something of fear” from enemies, “ and hunger” i.e. He will test 
    them with a little of both, because if He were to test them with extreme 
    fear or with extreme hunger, they would be doomed, but the point of trials 
    is to show this distinction, not to doom people. 
“loss of wealth” 
    this includes all kinds of loss of wealth such as disasters coming from the 
    heavens, drowning, loss, seizing of wealth by wrongdoers such as unjust 
    kings, banditry and so on. 
“lives” i.e. loss of 
    loved ones such as children, relatives and friends from various kinds of 
    disease in a person's body or in the body of those whom he loves. “and 
    fruits” means grains, the fruit of date palms and all other trees and 
    vegetables, due to hail or cold or fire or a catastrophe such as locusts and 
    the like. 
These things will 
    inevitably happen because the All-knowing All-aware has told us of them, so 
    they happened as He told us. When they happen, people fall into one of two 
    categories, those who panic and those who are patient. The one who panics 
    suffers two calamities: the loss of a loved one, which is a calamity, and 
    the loss of what is greater than it, which is the reward he could have 
    attained if he had followed the command of Allaah to exercise patience, so 
    he incurs loss and deprivation and a decline in the faith that he has; he 
    misses out on patience, acceptance and gratitude and there befalls him the 
    divine wrath which is indicative of great loss. 
As for the one whom Allaah 
    helps to be patient when these calamities come, he controls himself and does 
    not express discontent in word or deed; he seeks reward for that which is 
    with Allaah and realises that the reward he will attain by being patient is 
    greater than the calamity that has befallen him. Indeed the calamity is in 
    fact a blessing because it becomes a way to attain something that is better 
    and more beneficial. He has obeyed the command of Allaah and attained 
    reward. Hence Allaah says: “but give glad tidings to As‑ Saabiroon (the 
    patient)”, i.e. give them the glad tidings that they will be given their 
    reward without reckoning.
The patient are those who 
    have earned these great glad tidings and bountiful gift from Allaah. Then He 
    describes them as “ [those] who, when afflicted with calamity”, which 
    refers to everything that pains the heart or body or both, of those things 
    mentioned above. 
“[they] say: ‘Truly, to 
    Allaah we belong” i.e. we are slaves of Allaah, subject to His command 
    and control; we have no control whatsoever over ourselves or our wealth. If 
    He tests us with any of those things, the Most Merciful of those who show 
    mercy sas disposed of His slaves and their possessions, and there can be no 
    objection to Him; rather it is a part of a person's full and complete 
    submission and servitude to Allaah (‘uboodiyyah) to know that calamity has 
    come from the All-Wise, Who is more merciful to His slave than he is 
    himself, and that requires him to be pleased with Allaah and to give thanks 
    to Him for His decree, because that is better for His slave, even if he does 
    not realize that, as we all belong to Allaah, then to Him we will return on 
    the Day of Resurrection, then each person will be requited for his actions. 
    So if we are patient and seek reward with Him, we will find an abundant 
    reward with Him; but if we panic and get angry, there our lot will be no 
    more than divine wrath and loss of reward. So each person belongs to Allaah 
    and will return to Him, and this is one of the strongest means of being 
    patient. 
“They” i.e. those 
    who are described above as being patient “are those on whom are the 
    Salawaat (i.e. who are blessed and will be forgiven) from their Lord” 
    i.e. praise and speaking of their virtue. “and (they are those who) 
    receive His Mercy”, which is abundant. Part of His mercy towards them is 
    that He helps them to be patient, by means of which they attain the reward 
    in full. “and it is they who are the guided ones”, those who know the 
    truth, which in this context refers to their knowledge that they belong to 
    Allaah, that they will return to Him, and they act upon it, and that is 
    their patience for the sake of Allaah. 
This verse indicates that 
    the one who is not patient will have the opposite of what they have, so he 
    will be blamed by Allaah and punished, misguided and will suffer loss. How 
    great is the difference between the two groups and how little is the effort 
    of those who are patient, and how great is the pain of those who panic. 
These two verses tell us 
    that we should think about calamities before they happen, so as to reduce 
    their impact and make them easier to bear if they do happen, and explain how 
    to respond to them if they happen, which is with patience. And they explain 
    what helps one to be patient, the reward that the patient person will have 
    and they describe the situation of the one who is not patient, which is the 
    opposite of patience. And they tell us that these calamities and trials are 
    the law of Allaah and one can never find any alternative to the law of 
    Allaah, and they describe different kinds of calamities. End quote.
Tafseer al-Sa’di 
    (p. 75). 
Think about these words of 
    the Prophet (blessings and peace of Allaah be upon him) and these teachings 
    of the salaf: 

    it was narrated that there Mother of the Believers, Umm 
    Salamah (may Allaah be pleased with her), said: I heard the Messenger of 
    Allaah (blessings and peace of Allaah be upon him) say: “There is no Muslim 
    who is stricken with a calamity and says what Allaah has enjoined – ‘Verily 
    to Allaah we belong and unto Him is our return. O Allaah, reward me for my 
    affliction and compensate me with something better’ – but Allaah will 
    compensate him with something better.” 
She said: When Abu Salamah 
    died, I said: Who among the Muslims is better than Abu Salamah, the first 
    household to migrate to join the Messenger of Allaah (blessings and peace of 
    Allaah be upon him)? Then I said it, and Allaah compensated me with the 
    Messenger of Allaah (blessings and peace of Allaah be upon him). 
She said: The Messenger of 
    Allaah (blessings and peace of Allaah be upon him) sent Haatib ibn Abi 
    Balta’ah to me with his proposal of marriage, but I said: I have a daughter 
    and I am of a jealous nature. He said: “As for her daughter, we will pray to 
    Allaah to make her independent of her, and I pray that Allaah will take away 
    her jealousy.” 
Narrated by Muslim in his
    Saheeh (918). 
So pray to Allaah to reward you for your calamity and compensate you with someone better than her. Also pray to Allaah for this girl and for all the deceased Muslims, asking for mercy and forgiveness for them. 
And Allaah knows best.