All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we thank you for being keen on being kind and dutiful to your parents especially your mother, in addition to being keen on getting married and keeping yourself chaste. May Allaah reward you for that.
There is no doubt that the Sharee’ah clarified the true criteria in choosing a spouse which are religion and good moral conduct. Abu Haatim Al-Muzani narrated that the Prophet said: “If a man whose religion and moral conduct are pleasing to you proposes to you, then let him marry; otherwise there will be great mischief and corruption on earth. They [companions] asked: “What if he has something to be criticized about.” He [] said: “If a man whose religion and moral conduct are pleasing to you proposes to you, then let him marry (and he repeated this thrice)." [At-Tirmithi]
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Indeed, you did well by trying to convince your mother in a respectful and calm manner, and we advise you to continue doing so. First, you should seek the help of Allaah by supplicating Him earnestly, and then you should seek the help of some righteous people who may influence her. If she is convinced, then this is what is required, but if she insists on refusing and this man is suitable to marry you, then you are not obliged to obey your mother, and it becomes permissible for you to marry this man without her consent because obedience is required only in what is permissible and it is not among the permissible matters for a mother to prevent her daughter to marry someone who is suitable and competent.
If a girl gets advanced in age and she did not get married, then it is her who will be harmed and not her mother.
Moreover, since the noble Sharee’ah gives the right to a daughter to take her matter to the judge if her father prevents her to get married to a suitable man if he proposes to her for marriage, then she is allowed to marry without the consent of her mother with greater reason if the latter refuses to consent to her marriage to a suitable man.
Finally, we advise this mother to fear Allaah in her daughter and she should do what is best for her daughter and she should not look to the social differences and other matters that are not at all considered in the Sharee’ah.
Allaah Knows best.