Her mother approved of the fiancé then she rejected him. Is she sinning if she marries him?
Question

                I got married to a girl who is of good character and religiously committed. The girls’ parents are divorced. I approached the girl through her wali (guardian) and I was accepted by him and by her mother, but the mother felt some resentment towards me because I had approached through her ex-husband – the wali of the girl. Please note that my wife’s mother is mentally unstable. Her ex-husband told me about that, as did my wife. Between the marriage contract and the wedding party, my wife’s mother put pressure on my wife and insulted her, so we decided to bring the wedding forward. I asked her wali for permission to bring it forward and he gave me permission and set a date for the wedding. But the wedding happened to be on a day when the girl’s mother was travelling, and we knew that she would be travelling. We asked her several times to tell us the date when she would be travelling, but she did not tell us anything, even though she knew the date when she would be travelling and when she would be coming back. My wife asked me to delay the wedding until her mother came back, but I refused, as did her guardian, because the longer the wedding was delayed the more problems there would be. It became clear to me that my wife’s mother was trying to make me divorce my wife. The wedding went ahead in the absence of my wife’s mother, some of her sisters and one brother. Later on, we found out that my wife’s mother and her oldest sister had urged my wife’s brothers and sisters not to attend, and my wife’s brothers and sisters had divided into two groups, those who did not pay any attention to this agitation and those who went along with it. After the wedding, there was a cutting off of ties between my wife and her mother and her sisters. They accused my wife of disobeying her mother and they accused me of inciting her to disobey her mother.

My question is: If we assume for argument’s sake that my wife’s mother rejected me as a husband for her daughter, but her wali agreed and encouraged his daughter to accept me, is the fact that my wife did not obey her mother regarded as disobedience? What if I have a dispute with my wife’s mother and my wife finds herself in an awkward situation – who should she obey, her husband or her mother?.
Praise be to Allah.Firstly: 
We ask 
    Allaah to bless you and to join you together in goodness, and to bless you 
    with righteous offspring. 
Secondly: 
If the 
    matter is as you describe, and your wife’s mother is suffering from 
    psychological problems, and she approved of you at first, then there is no 
    sin on her daughter for going against her and agreeing to marry you, so long 
    as her wali approved. 
She has to 
    strive to honour her and to uphold ties of kinship with her, and to maintain 
    a good relationship with her sisters, even if they mistreat her, because 
    ties of kinship are an important matter. The one who upholds ties of kinship 
    is not the one who returns like for like, rather the one who truly upholds 
    ties of kinship is the one who maintains those ties even if his relatives 
    cut him off, as the Prophet  (peace and blessings of Allaah be upon him) 
    said. 
Thirdly: 
If there is 
    a conflict between obeying one's parents and obeying one's husband, then 
    obeying one's husband takes precedence, because of the greatness of his 
    rights over his wife. The Prophet  (peace and blessings of Allaah be 
    upon him) said: “If I were to command anyone to prostrate to anyone else, I 
    would have commanded women to prostrate to their husbands, because of the 
    rights that Allaah has given them over them.” Narrated by Abu Dawood (2140), 
    al-Tirmidhi (1853) and Ibn Maajah (1853); classed as saheeh by al-Albaani in
    Saheeh Abi Dawood. 
Ahmad 
    (19025) and al-Haakim narrated from al-Husayn ibn Muhsin that a paternal 
    aunt of his came to the Prophet  (peace and blessings of Allaah be upon 
    him) for something she needed, and when her need had been met, the Prophet 
     (peace and blessings of Allaah be upon him) said to her: “Do you have a 
    husband?” She said: Yes. He said: “How are you with him?” She said: “I do 
    not fall short in giving him his rights except what I am unable to do.” He 
    said: “Pay attention to how you are with him, for he is your paradise and 
    your hell.” Classed as saheeh by al-Albaani in Saheeh al-Targheeb 
    wa’l-Tarheeb (1933). 
Imam Ahmad 
    (may Allaah have mercy on him) said concerning a woman who had a husband and 
    a sick mother: Obedience to her husband is more essential than to her 
    mother, unless he gives her permission. Sharh Muntaha al-Iraadaat 
    (3/47). 
But your 
    wife should honour her mother as much as she can, and you should help her to 
    do that. 
And Allaah 
    knows best.