How do we balance keeping a peaceful home and caring for my MIL who won't comply with medical professionals?

First, I hope this finds all caregivers in good spirit today! Please excuse this writing if it seems scattered, I am writing it from my heart and it is racing right now from disbelief and "wits end" feeling.
My MIL is 75 y/o and was in ICU many weeks (Oct 13, 2012- December 18, 2012) for a near fatal C-diff infection, she then went to rehab centers and got kicked out of every one due to threats she made against employees and non-compliance (refusal to participate in her healing process) she has been in our home since January 30, 2013. In an effort to understand which diseases she had and how best to care for her in our home she got the best testing by the best specialists and we were floored to learn that all these "diseases" she has been using to justify her laziness for the last 20 years were lies. Other than the C-diff, she is in perfect health. Now that she is out she refuses to follow Dr. orders, refuses to do her Physical Therapy and calls people to say my husband and I are denying her food, refusing to heat the house and if she goes to a Dr. appointment that we said we will pack her stuff and rent her room out. We know it isn't true, but it still doesn't feel good.
Her behavior isn't due to physical and/or mental illness and we know that because she was like this before she got sick, what is angering her is until she came to live with us, people just sympathized, blindly believed her and my husband and I aren't like that. We don't allow that negativity and manipulation in our home, we expect honesty from anyone under our roof and we aren't afraid to ask her to "connect the dots" on these stories that make no sense at all. She says that she has never had anyone make her responsible for her words/actions.
We truly believe she should be an inpatient somewhere, in the one month she has been home her strength has declined to a very scary point because she refuses to follow home health instructions. When we remind her or offer to do exercises or walk with her, we get screamed at. She claims "bad knees" but we know that isn't the case. We hear her on the phone telling her friends she hopes to get sick enough to go back "on vacation" in the hospital.
She is not a "pouter" she is a screamer, blamer, manipulator and our home until now has been a happy peaceful loving place. The stress is going to kill my husband and I. I am 6 weeks away from ending a long chemo course that exhausts me and the other 2 adult children who live locally refuse.....flat out refuse to help out. I never realized how smart they are.