To answer your question, we'd need to know more about you and the circumstances.
I do have some questions:
Do you and your mother-n-law get along?
Does your husband and his mother get along?
Do you work?
Does your m-n-law drive?
Does she have her own car?
Would you be responsible for driving her places?
Do you consider your home your domain?
Do you have room enough in your home to hide away if need be?
What personality type are you?
What personality type is your husband?
What personality type is your m-n-law?
Do you have a way to give her a phone of her own?
Do you have a way to give her her own TV viewing area?
Can you possibly giver her a kitchenette?
Is she ambulatory?
Is she incontinent?
Is she on medication?
So many questions....
I can say that we tried it with my m-n-law and it did not work for us.... for many, many reasons.