You're screwed. Anything you do other than just give her you half you will become the bad guy. Give her you half and walk away. If you force a sale, she will likely destroy the house just because she can. If you set up a mortgage with her paying you, she will stop paying, and again, you will be the bad guy because you will have to evict your own sister. Likely she cannot buy your half with a lump sum. It's a no win all the way around.