When in doubt, don't. You are under no obligation to leave your child anywhere you aren't absolutely sure she's safe!

I wouldn't broach the subject with "mom" either. If you don't give her any ammunition, she can't fire it back at you. If you show your "hand" in this, she might hide her nastiness in front of you, and still be unsafe with your child. Silence would be golden on this, imo.

But, if you are concerned for her own health, then by all means approach her on that... maybe more is going on with her, and maybe she doesn't even know it. If you can help her seek more help then do so, but again, I wouldn't mention the fear of her being with your child.