Is it possible to return to this world to do righteous deeds?
Question

                My sister is dying, and she probably will not live through next month; only Allaah (SWT) knows. She has done many things in her life that she has bitterly regretted and sincerely repented for, and she is always wishing she could go back in time and correct the past. She told me she wants to know one thing before she dies: Will those who are blessed by Allah's mercy and granted the eternal Jannah, since they will be given anything and everything their heart so wishes in the Hereafter, be able to somehow go back in time, back into the earthly past by Allaah's leave and correct their own and others' grave worldly mistakes and wrongdoings, by having their own special personal world in Jannah? Allaah (SWT) has said about the believers' Jannah: "I have prepared for My righteous servants that which no eye has seen, no ear has heard, and it has not crossed the mind of man. Recite, if you wish: ‘No person knows what is kept hidden for them of joy’". Allaah (SWT) will give those who dwell in Jannah rewards that they have not ever even dreamed of; therefore, will He give them that which had crossed their minds in this life but could not have, and my sister's wish in particular? Please, please answer as quickly as possible. This is terribly distressing to my sister, and she most likely will not live past the next few weeks. Only Allaah (SWT) knows. Please help, and may Allaah (SWT) bless you in this life and the next.
Praise be to Allah.
    Firstly: 

    You should note, may Allaah bless you, that people’s life 
    spans are in the hand of Allaah, Who says (interpretation of the meaning): 
“For everything there is 
    a time prescribed”
[al-Ra’d 13:38 - 
    Pickthall] 

    “and no person knows in what land he will die”

    [Luqmaan 31:34]

    It is not possible for anyone to know when he will die; it is 
    only speculation which may be proven true or may be proven false. 

    Sickness – for example – does not mean that a person will die 
    soon, just as being young and strong does not mean that a person will live 
    for a long time. 

    How often have people assumed that a sick person will die 
    soon, then he has lived for a long time. And how often has death come 
    suddenly to a healthy person. 

    The poet spoke the truth when he said:

     Equip yourself with piety, for you do not know, when night 
    comes, whether you will live till dawn.

    How many young men laugh in the evening and the morning, when 
    their shrouds have been prepared but they do not realize?

    How often do people hope for a long life for young people, 
    then their bodies enter the darkness of the grave.

    How many brides have been adorned for their grooms, when it 
    has been decreed on Laylat al-Qadar that their souls are to be taken.

    How many healthy people have died for no reason, and how many 
    sick people lived for a long time. 

    What is required of the believer is to prepare for death at 
    any time, by repenting to Allaah and doing righteous deeds. Ibn Maajah 
    (4259) narrated that Ibn ‘Umar said: I was with the Messenger of Allaah  
    (peace and blessings of Allaah be upon him) when a man from among the Ansaar 
    came to him and greeted the Prophet  (peace and blessings of Allaah be 
    upon him) with salaam, then he said: “O Messenger of Allaah, which of the 
    believers is best?” He said: “The one who is best in attitude.” He said: 
    “Which of the believers is most wise?” He said: “The one who remembers death 
    the most, and is best prepared for what comes after it. Those are the wise.” 
    Al-Iraaqi said: its isnaad is jayyid. It was classed as hasan by al-Albaani 
    in Saheeh Ibn Maajah. 
Who 
    has guided your sister to repent and to regret what she has done in the 
    past. 
    
    We send her the glad tidings that if she is sincere in her 
    repentance, then Allaah will accept her repentance and will turn her bad 
    deeds into good deeds. Allaah says (interpretation of the meaning): 

    “Except those who repent and believe (in Islamic 
    Monotheism), and do righteous deeds; for those, Allaah will change their 
    sins into good deeds, and Allaah is Oft‑Forgiving, Most Merciful”

    [al-Furqaan 25:70]

    See also question no. 
    14289 

    Secondly: 

    When the believer enters Paradise, Allaah will give him all 
    that he wishes for, and more than he wishes for. Allaah says (interpretation 
    of the meaning): 

    “Trays of gold and cups will be passed round them; (there 
    will be) therein all that inner‑selves could desire, and all that eyes could 
    delight in and you will abide therein forever”

    [al-Zukhruf 43:71]

    Al-Bukhaari (806) narrated from Abu Hurayrah and Abu Sa’eed 
    al-Khudri (may Allaah be pleased with them) in a lengthy hadeeth that the 
    Prophet  (peace and blessings of Allaah be upon him) told them of the 
    last of the people of Paradise to be admitted to Paradise. Allaah will say 
    to him:  

    “Tell Me your wishes.” So he will say all that he wishes for, 
    and Allaah will prompt him to mention other wishes and when he cannot wish 
    for any more, Allah will say “You will have that and a similar amount 
    besides.” Abu Sa’eed al-Khudri (may Allaah be pleased with him) said to Abu 
    Hurayrah, The Messenger of Allaah  (peace and blessings of Allaah be 
    upon him) said, “Allaah said, ‘You will have that and ten times more.’” Abu 
    Hurayrah said, “I only remember the Messenger of Allaah  (peace and 
    blessings of Allaah be upon him) saying, ‘You will have that and a similar 
    amount besides.’” Abu Sa’eed said, “I heard him saying, ‘You will have that 
    and ten times more.’” 

    But if a believer wishes to go back to this world then he 
    will not be granted that, because Allaah has decreed that no one will go 
    back to this world. 

    Allaah says (interpretation of the meaning): 

    “And a ban is laid on every town (population) which We 
    have destroyed that they shall not return (to this world again, nor repent 
    to Us)”

    [al-Anbiya’ 21:95]
i.e., the people of the 
    towns that Allaah has destroyed will wish to go back to this world so that 
    they can make up for what they missed. 

    See Tafseer al-Sa’di, 868. 

    Al-Bukhaari (2817) and Muslim (1877) narrated that Anas ibn 
    Maalik said: The Prophet  (peace and blessings of Allaah be upon him) 
    said: “No one who enters Paradise will wish to come back to this world, even 
    if he were to be given all that it contains, except for the martyr, who will 
    wish that he could come back and killed ten times because of the honour that 
    he sees.” 

    But that wish will not be granted to him. 

    Al-Tirmidhi (3010) and Ibn Maajah (190) narrated that Jaabir 
    ibn ‘Abd-Allaah ibn Haraam said: “The Messenger of Allaah  (peace and 
    blessings of Allaah be upon him) met me on the day of Uhud and said: ‘O 
    Jaabir, shall I not tell you what Allaah said to your father?’ I said: ‘Yes, 
    O Messenger of Allaah.’ He said: ‘Allaah has never spoken to anyone except 
    from behind a screen, but He spoke to your father directly and said: “O My 
    slave, ask something from Me and I shall give it to you.” He said, “O Lord, 
    bring me back to life so that I may be killed for Your sake a second time.” 
    The Lord, may He be glorified, said: “I have already decreed that they will 
    not return to life.” He said, “My Lord, then convey (this news) to those 
    whom I have left behind.” Allaah said:

    “Think not of those as dead who are killed in the way of 
    Allaah. Nay, they are alive, with their Lord, and they have provision”

    [Aal ‘Imraan 3:169].’” 
Classed as saheeh by 
    al-Albaani in Saheeh Ibn Maajah. 

    We ask Allaah to bless your sister and all the Muslims with 
    sincere repentance. 

    And Allaah knows best.