What Do You Do?

I have a friend who has a 4 months old daughter. She broke up with her kid's dad because he was using crack but then she got with another guy who ended up using meth. Me and a few other girls told her to leave him and she did. But now she wants to get back with him because "he's been clean for a week and he promised this time" I told her to just be his friend and forget a relationship because addiction is a powerful thing especially when it's a hard drug like that and she's got a little baby. Drugs shouldn't be around kids period but they really shouldn't be around a baby. She basically told me she didn't care and she was gonna get back with him. If she comes to me and says he's using again and they're still together I'm gonna call CPS. Would I be wrong? Should I try to talk her out of dating him again or should I just let her dig her own hole? I honestly don't care about her feelings I'm more worried about the baby.