Dilemma

So I’m in a little bit of a pickle. My venue is booked and I already have in mind who I want to be in my bridal party. Obviously the right thing to do would ask my sister to be the maid of honor. But here’s the thing. She’s a drug addict. She’s in rehab now and has been since September and after that goes to a halfway house. She’s been using since she was like 14 and is 26. She just got caught using while she was in rehab! I just don’t know if she is someone I want or can trust to help me with my wedding. The longest she’s been clean is a year and a half and that’s because she was away at teen challenge in Virginia and away from all the scumbags she knew. I know if I don’t ask her. My dad is going to be mad. But if she can’t keep her life straight why do I need someone like that playing a big part in my bridal party. Am I in the wrong for feeling this way?