How do I deal with Mom?

My Momma is being a little difficult here. My kids and I visited her yesterday and she said she doesn't want me to do anything about their bickering/arguments in her house. My daughter was throwing a kicking fit about something and threw her shoes up against a wall then threw herself on the floor, so I picked her up and sat her down in a chair and told her to straighten up and apologize or we're going home..and I really meant it. Well my mom she got upset with me and said it's the same thing as hitting them and she doesn't like their fighting but she doesn't want me to get involved in it either. I said I'm their mother, somebody has to discipline them. My mom is just the opposite now because when my brother and I were little her and Dad hit us with a razor strap (big strip of leather) which I DO NOT do to my kids. So now she doesn't want any form of discipline done at her house. Only she can't see that they only act like brats at her house 'cause she lets them get away with everything. Whew! That was a mouthful. Thanks.