I can't take it any more

My husbands ex(baby mama) has been talking to a chick that she had no idea knew me. It was at a gym I used to work at . I also go daily. The ex found out I go to this gym so she now drives to mine. When she lives no where near us. She is telling the trainer literally things that aren't even true since she barely knows me. Also telling the girl her and my husband were trying to get back together. I'm livid. 
I want to say something to her but I know I won't be able to stay calm so I told hubby to talk to her. He says it's high school drama he doesn't want to get involved. I'm pissed. Do I confront her or just let her Keep talking or let her keep sounding stupid.