Yes, they can.

Yep, they can. She signed an agreement to pay 6 months of rent. Whether or not she stays there during that 6 months is not their concern, they just want the money.

Yes, they can sue for balance of the lease, unless you get a replacement tenant that they will allow to take it over. Money is the bottom line. NOTE I did not say they can GET the money. I was a landlord, and I am a disabled person. Here's the gig: They can sue, she can appear in court and plead the case to the judge. It may make a difference. If she blows it off, the judge awards judgement to the landlord. End of argument. BUT, the burden of collecting is on the landlord :-( so he/she is probably better off to let this go, and save the court costs and aggravation. Take pictures, and make sure to save any receipts for cleaning the place when she leaves. No court will let the landlord take your sister's Disability pay. She *may* have to make some small payments on the bill, but she will not be robbed blind by the court. :-) FYI - get a Disability Attorney, ASAP!!! Like yesterday. Otherwise you will lose the first appeal or 2 to Disability, and about 12-18 months of time with no income. Sad but true. They are there to make you go away, not help the citizens. (my lawyer said this) So even though it will cost a percentage of what her settlement is - GO for it with the lawyer. Good luck.

Absolutely. If she can't perform on a contract to which she had agreed. She faces the possibility of multiple legal repercussions. Have her negotiate the situation with the landlord or property manager.