Wow I thought my folks were bad, they seem normal by comparison...
Seriously, some mums will never accept any woman is good enough for their son. I have one of them.
All I can suggest is either an intervention, some doctor or psychiatric help or just all out confronting her to get her to back off. I went the other
way and keep my family and relationships separated and private. If my mother starts to intervene I flatly tell her to butt out, although she is
nowhere near as extreme as that. About the only other possibility is to move far enough away that the effects aren't as close by.
If you aren't prepared to change it, then the problem will just compound itself.