Originally Posted by CaptainForest
Fr Chuck's advice about putting your name on the deed as well is a good idea.
However, I wish to point out a caution for your mother.
Since your sister's name is on the deed, if she gets into financial trouble, they can come after all her assets (and that includes your mother's house).
And the same will then apply if your name is on the deed.
Your best option is to remove your sister, but if that is going to be too much of a problem and you feel like you sister is ok financially, then go ahead and have your name put on the deed.