My ML has been living with a relative for the last 7 years, they wanted her there to keep the relative's aging mother company. Now the mother has died, and the relative doesn't want the ML any longer.
Can the relative force us to take her or pay for her care now?
You might want to offer some suggestions to the relative, depending on what condition your MIL is in. Can she live independently? How old? Dementia?
If she can live alone, they can get her into senior housing. Help her sign up for a home aide if needed and meals on wheels, etc.
However if she's helpless and prone to eviction soon, you might feel morally liable to take her.
Has this caregiver been receiving compensation for caring for MIL?
What level of care does MIL require?
You can ask for a "needs assessment" by her local Area Agency on Aging who may also be able to help you identify good facilities that would meet her needs if you don't desire to bring her home.