My mom's been slapping my child. How to handle?

My mother has always had a very short temper -- she would yell over the littlest things, and slapped me in the face on numerous occasions as a child and teen.After a long time without a huge amount of contact, she moved close by after my daughter was born. We still don't spend a ton of time together, but she babysits occasionally, including a few multi-night getaways. I've heard her yell at the kids (almost 8 and 3), which bothers me, but thought that was the end of it.Last night, while my daughter (8) was in the bath, she started asking me questions about my mom... First, random ones, like "what color was her hair?" Then she asked me, "did she ever slap you?" I was taken aback by that, and answered honestly, yes, and asked if she'd slapped her. I'd NEVER mentioned it to my daughter, as I wanted her to have a positive relationship with her grandmother, and really thought my mother would never go there with my own kids... But apparently that's not the case.I am feeling really disturbed by this. My husband and I have already asked her to help with a few upcoming commitments, and I'm honestly wondering whether we can trust her at all at this point. How should I address this? I'm not sure if I need to issue an ultimatum or really just assume this relationship is just as toxic as it was in my childhood and do my best to get my kids away from her. Thoughts, advice? via /r/Parenting http://ift.tt/2vCwhRH