Blended family question!!!?

Hello, I am a wife in a blended family. My 1, his 3, & our 2. (6 kids total). Well his exwife is still very much involved with their kids, but she does mean things like hit my 2 yr old, say rude comments about my teen (unbeknown to her), and calls CPS on my hubby. She is bitter and vindictive and acts out when she can't get her way with my hubby. Yesterday she took 3 girls to a bball event and I had to tell my daughter that she could not go with. It wasn't hard for me not to send my kid with her, but they fact that she could not be with her sister hurt me and her. I have let her go with her sis in the past, but this women continues to lash out at me, my hubby, and our kids and then pulls this supermom stunt by doing things that make her go unsuspected. None of the parents in our circle know what she's been doing and she shows up to functions all dolled up with drinks and treats, but they dont' know that she just called CPS on us two weeks ago, and hit my two year old a few months ago as well. How do I get my daugther to understand that I can't send her along with this wolf in sheeps clothing. And do I just keep my my shut at functions, or tell her off and remove her facade in front of all these other people who she's jocking for position with. Her kids live with us part-time, but she wants to put on the impression that they don't so she forces herself in the inner circles that we've established, she never pays for any fees, and she continues to mistreat us when she's out of sight of other parents. My daughter just thinks I am being mean, but I don't trust this lady around my children.