Reminds me of the saying, "No good deed goes unpunished." How is it that your sister is so clueless? Does she have a history of taking advantage of other people? Or is this totally new behavior? In any event, if your sister's name is not on the lease or rental agreement, then you are going to have to go through the formal process of having her evicted. You start the process by giving your sister written notice that you are evicting her. If her name is on the rental agreement, then you cannot evict her, and you will have to move out to get her out of your living quarters.
Or perhaps you can talk with your landlord and ask your landlord to evict your sister because there are too many people living there. Perhaps the rental agreement does not permit anyone else to live there without the landlord's permission. This will probably destroy your relationship between you and your sister, but at this point, you are likely beyond worrying about it.
I am going to add a tag of landlord/tenant law because that is really what this case is about. This will put your query out to attorneys who handle this area of law on a regular basis. I do not handle landlord/tenant law, although I do know some things about it.
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Not sure from your question whether you own the house or is you are renting the home. If you own the home then give your sister a notice to quit letter giving her 30 days to move out. The you seek possession and file complaint for tenant holding over. If you rent then your landlord must do the above and he has authority to evict her or potentially evict you too. Please call my office to discuss your options.