Should I forgive my sister? (Long…sorry)?

My sister (7 years older than me) has always been the “bad” one. Jail, drug addictions, numerous rehab centers, etc. She is the stereotypical lying, cheating, stealing at anyone’s expense to get what she wants. She has screwed me over so badly. I’ve tried so hard to keep forgiving her and trying to help her. I eventually realized that I can’t help her, and it was starting to wear me down emotionally. I have this whole, “Just because she’s my sister doesn’t mean I have to love her or claim her.” attitude that a lot of people don’t understand.
She’s in rehab again, and I don’t know if I should go see her. She always supported me when I was in treatment for my eating disorder, but I never screwed people over the way she has. What do you think? Should I visit her and give my full support? Should I be skeptical, but go see how she’s doing? Thanks.