What to do when other child hit/pushes your child(toddlers)?

I was at the park yesterday with my 17 month old girl having a blast. All of sudden this girl probably around 2 years old starts following us everywhere we go. She tried pushing my daughter off the balance beam(I had her hands so she didn't fall)so we went to the slide. She followed us and pushed my daughter again as she was climbing up the stairs.Then we went to another thing and she hit my daughter multiple times because she wanted to do what she was doing.I didn't know what to do and my daughter was so confused(she's never been hit or pushed and we taught her young not to hit!) so she just yelled no at her over and over but didn't hit or push back until I took her from the situation again. At this point she followed us again and started hitting and pushing then the mom finally showed up(she was too busy with her two other kids who were older and also terrorizing the playground)and just said no and let the girl keep pushing my daughter and hitting her so we left(which caused my daughter to be very upset because she wasn't done playing yet!) what would you have done? I really wanted to chew the mom out but I don't like acting like that in front of my daughter. It doesn't set a good example but neither does letting another child hit or push her! I just don't get why people can't discipline their children. I would never let my daughter keep hitting and pushing another child! via /r/Parenting http://ift.tt/2e4CCCH