How can a mother be such a jerk to her daughter?

Well maybe you should take your ex a side and tell her that the time she spends with the children should not be yelling at them the whole time. Now for the clothes you should talk with your daughter before she goes out and gets laughed at. This will hurt more then just you laughing and not saying anything because she will turn it around on you and say "Why didn't you tell me"? Because of you I got laughed at today it's all your fault. Been there and done that!