Thanks for the help everyone. She is on a month-to-month lease right now. I've asked her to sign a new lease but she hasn't done so and I don't think she wants to commit for another year. They've had a few set-backs financially and I've already had to help them out several times. I had to tell her that they are now on their own after this last bailout. I do worry about her but I can't continue to be her safety net and I hate the thought of being in debt to anyone. I thought about writing a letter to the landlord and sending it certified mail but didn't know if that would be binding. Plus, I don't want to force my sister into signing another lease for a year. I guess I'm just stuck.
As we must account for every idle word, so must we account for every idle silence." ~Benjamin Franklin