Am I wrong for holding my MIL's past against her?

My MIL used to do drugs and worse she used to do them with my husband when he was as young as 12. He was severely addicted to drugs. She would shoot him up and she almost killed him at one point. I don't allow my kids alone with her and my husband feels the same way. She's hurt by this and said she doesn't understand why we are using her past against her. Here's my thing. I don't think it's always wrong to use someone's past against them. If they did something they didn't hurt anyone or only hurt themselves that's one thing. But something like child abuse because shooting up a child is child abuse or any type of abuse you have to accept that those choices may effect you forever. You made the decision to do drugs with a child. Even if it was a long time ago sometimes you have to accept that some people will never trust you fully and imo people who have really changed realize that. If you can't realize that not everyone has to forgive you and trust you when you did something REALLY bad then maybe you haven't really changed.

@S my husband just simply doesn't trust her alone with our children. The problem isn't her addiction. My husband was an addict. But I know PLENTY of ex addicts who NEVER gave their children drugs. There is 0 excuse for that. There's being an addict. And there's shooting up your child with heroine. The whole reason she's upset is because she can not be alone with our children. And sadly that's the price you pay when you give children drugs. She believes not being allowed to be alone with our kids is holding it against her. No she's not allowed alone with them. They will never spend the night at her house. And that's a boundary we set.