Is there a VRBO rental near you? A friend has her parents stay for 1 month and they rent a studio apartment through VRBO. Even if you MIL doesn't drive, I would be willing to go pick her up in the morning say 10am and drop her off after dinner...6pm. If it's close to places where she can walk, she can find things to occupy herself too.
1-2 months..heck no. And it sounded like you were TOLD she would be there for 1-2 months and not asked. Wouldn't fly in my house.