If you cannot convince your mother about this marriage, your going ahead with it will make her angry and will mean that you will lose her, as you say. So what you must do is obey her by not marrying this woman, unless you fear that you will fall into zina with her, Allaah forbid.
This is based on the fact that obedience to the mother is obligatory, whereas marriage to a particular woman is not obligatory. There are many women, hence Ibn al-Salaah, al-Nawawi and Ibn Hilaal stated – as mentioned by the great scholar Muhammad Mawlood al-Mauritaani in Nuzum al-Buroor – that it is obligatory to obey one's father if he forbids marriage to a particular woman.
But if you think it most likely that you will fall into haraam, then warding off that evil takes precedence over obeying your mother.
Our advice is to let reason prevail over emotion and to look for another woman with whose religious commitment and character you are pleased. It is better if she is a virgin and young enough to have children. Thus you will achieve a number of interests, the greatest of which is pleasing your dear mother who has sacrificed her own interests for the sake of raising you. You will also be keeping the family together, and producing children, which is one of the aims of marriage.
Pray to Allaah a great deal, asking Him to guide you aright.
And Allaah knows best.