Help... i think i hate my best friend...?

Back in September I came to this knew school where I didn't know anyone, so did this girl named Stacy. One day my new friend introduced me to Stacy and we just clicked. Ever since then we were inseparable. We would be together almost every day, we became best friends. After a couple of months, my two close friends and I realized something was going on. Our stuff went missing and every time it did, just so happened she would have it! We didn't want to confront her because we knew of things that happened to her in the past that caused her to have self esteem and self confidence issues. Also every time we tried to see if she would confess by saying things like "Oh is that my blush?" she would begin to stutter and panic saying that her mom got it for her and asked if we think she stole it. She would also manipulate us by using what we called her 'whiny voice', which she uses to make us feel guilty to get her things such as money, food, clothes etc. We all knew what was going on but didn't want to confront her because of her issues. One day she confessed to one of the three of us to all that she's done. But she told that one friend she didn't want to tell me, and that really hurt me being the closest to her out of us three. So I confronted her myself. Ever since then I can't stop hating her. Her face, her perfume, her hair, the way she talks, everything about her makes me want to punch her in the face. She makes me feel so betrayed, and used, and angry. I talked to my counselor about it and she said it was because I've kept this bottled in for such a long time and also because I tried to giving her out occasionally by telling her that she can tell me anything constantly that it turned into hate. I told her I needed space and so did my other two friends but they slowly became close with her again. They told me she's changed like she said she would try to. But I couldn't believe it. Then I decided to give her a chance but she hasn't been proving herself to me. Yesterday I found out she took my bathing suit with her on vacation. She says she accidentally took it but she would've texted me the moment she found out she had it and ask for permission. Not only that but I found out through a facebook photo. I hate her more than ever know and I need to let go of all this hate. Help?