Myself and my partner and his sister are living in a house together and every time we leave the house she goes through our stuff and breaks things and steals things she has her stuff in our room as well as the rest of the house! Has anyone got any ideas on how to get her to move out!

Yes, evict her.

I understand unwanted roommates, and it is not always easy to evict them or possible. Start by moving her stuff out of your room and public rooms (within reason; some things need to stay in the bathroom, etc.). I'm assuming either one or both of you have spoken to her about her nasty little problems? If not, do it. Communication, communication. Other than that, I cannot really help you; in the past, I have lived with people like that and let them drive me crazy while I silently began to resent them. I just want to say, don't let that happen to you. It's probably not a healthy habit.

Do any of you own the house or are you renters? If owners, who is on the deed? If renters, who is on the lease?

Is your partner in agreement about getting her out?

In the interim, can you put locks on your personal spaces to prevent her from going through your stuff?