She has become Muslim and he wants to marry her but his mother refuses
Question

                I m in a great mess up, where, which to choose. I was in love with a christian girl, now she embraced islam. I want to marry her with my parents wish, which is not possible. My parents not at all ready to accept our relationship. I too doesn't want to hurt my mother(father deceased). Because she's the one who enlightened me to understand Allah the almighty. She struggle for us a lot. So, I prayed isthikara namaz to know what Allah wills for me. First time I saw the girl whom I want to marry,unfortunately next time I saw somebody else. I cannot judge myself what should I do. Whether to go against my mother & marry her or to give her up when she need me in desparate(She is newly converted muslim). I m afraid that leaving her may be make her to revert back to past life. I trust that she will not do, but the circumstances makes a person which they never wills. I am at an end neither swallow nor throw it out. So I want you to suggest me a way where I can keep both of them happy.
Praise be to Allah.We suggest that you should continue in your 
    attempt to convince your mother to accept your marriage to this girl. If she insists on refusing then it is good for you to obey your mother and 
    do as she wishes. There are many women and a man does not have to marry a particular woman. So obedience to your mother should take precedence in 
    this case, because that means that you will be honouring her and treating her kindly. Allaah says (interpretation of the meaning): 
“And your Lord has decreed that you 
    worship none but Him. And that you be dutiful to your parents. If one of them or both of them attain old age in your life, say not to them a word 
    of disrespect, nor shout at them but address them in terms of honour”
[al-Isra’ 17:23]
Ahmad (15577) narrated that Mu’aawiyah ibn Jaahimah came to the Messenger of Allaah  (peace 
    and blessings of Allaah be upon him) and said: “O Messenger of Allaah, I want to go and fight (in jihad) and I have come to consult you.” He said, 
    “Do you have a mother?” He said, “Yes.” He said, “Stay with her for Paradise is at her feet.” 
Shaykh Shu’ayb al-Arna’oot said: its isnaad 
    is hasan. 
It was also narrated by Ibn Maajah (2781) as 
    follows: “I went to the Messenger of Allaah  (peace and blessings of Allaah be upon him) and said, ‘O Messenger of Allaah, I want to go for 
    jihad with you, seeking thereby the Face of Allaah and the Hereafter.’ He said, ‘Woe to you! Is your mother still alive?’  I said, ‘Yes.’ He said, 
    ‘Go back and honour her.’ Then I approached him from the other side and said: ‘O Messenger of Allaah, I want to go for jihad with you, seeking 
    thereby the Face of Allaah and the Hereafter.’ He said, ‘Woe to you! Is your mother still alive?’  I said, ‘Yes.’ He said, ‘Go back and honour 
    her.’ Then I approached him from in front and said, ‘O Messenger of Allaah, I want to go for jihad with you, seeking thereby the Face of Allaah 
    and the Hereafter.’ He said, ‘Woe to you! Is your mother still alive?’  I said, ‘Yes.’ He said, ‘Woe to you! Stay by her feet, for Paradise is 
    there.’” This hadeeth was classed as saheeh by al-Albaani in Saheeh Sunan Ibn Maajah. 
Ibn Abi Shaybah narrated in his Musannaf 
    that Abu Talhah al-Asadi said: I was sitting with Ibn ‘Abbaas and two Bedouins came to him and spoke with him. One of them said: “I was looking 
    for a camel of mine and I stayed with some people. I liked a girl of theirs so I married her, and my parents swore that they would never accept 
    her. I swore that I would free a thousand slaves give one thousand gifts and slaughter one thousand camels if I divorced her.” Ibn ‘Abbaas said: 
    “I am not going to tell you to divorce your wife or to disobey your parents.” He said, “What should I do with this woman?” He said: “Honour your 
    parents.” 
Something similar was narrated from 
    Abu’l-Darda’. If this had to do with divorcing a woman after marrying her, it is more apt that you should obey your mother before marriage takes 
    place. 
And Allaah knows best.