Edit: I talked to a lawyer that I work with and got some advice, thanks though!
I'm sure it's hard to watch, but the ball is really in your M-I-L's court. Is she ready to sever this relationship? Will she have enough support from friends and family to go it alone if she gets out?
Regarding the loan, I'd guess it's time to consult a lawyer.
Good luck!
In short, no, there is nothing that you can do to have her removed from the loan just because of the circumstances. Short of convincing FIL to refinance and remove her name from the loan, possibly with either a cash incentive or legal threat, you're looking at taking legal action, and it may be hard to prove MIL's lack of mental facilities at the time, and likely will not be worth the cost (but IANAL).
You'll need to log in to post.