I'm so sorry about what's happening. At least she caught herself early on. My ex's sister was in a similar situation, except she'd been using for a long time. She dropped her son off at Grandpa's, and went to a rehab center- after my ex told her that if she didn't, he would call child protective services.
If you want anyone to talk to, please PM me. I've seen what you're seeing, and the best people to talk to are those who have experienced the same thing.