Now I'm angry

[Petie]

So, my mom moved in with us a few years ago. Then she went to live with her boyfriend who cleaned out her savings and then left her so she moved back in. My dd is a handful. We all know this, but tonight, I find out that my mother slapped her because she was cursing in my mother's face. I could understand if she didn't know any other way to deal with it, but I DID. I have fully explained how to deal with dd's behaviors and my mother agreed to abide by our standards. Then she goes and slaps my child. This apparently occurred a couple weeks ago and I only found out tonight because dd was cursing and DS 6 yr. old, said, "grandma slaps for that, maybe that will work". So, mom depends on us 100% for her financial needs. She has no money to get a place of her own or even buy groceries for herself. She gets a total of $800 a month and most of that goes to bills that her boyfriend racked up in her name. How do I deal with this?? It does explain the recurrence of dd's aggression over the past couple of weeks. Now she doesn't even feel safe at home.

(dd has been dxed with ADHD, ODD, and possible anxiety, she reacts aggressively and as I said, it's a handful)