Most Helpful Girl
Yes. You tell her to get the fuck out of your house.
Why are you having discussions about your child with her present? She's your ex's "problem", not yours.
Tell her to piss off and let the actual parents sort shit out. She's just a third wheel in this situation and it's not her place to butt in.
I understand that perhaps your ex wants her to be there or whatever, but ultimately she's out of line and needs to mind her own business.1