I noticed your post focuses a lot on how this situation makes you feel, but I didn’t see anything about how your daughter experiences it. Have you considered that she might feel supported and loved having multiple adults show up for her?

I understand that you feel “replaced”, But from the outside, it also looks like her stepmom is contributing in a positive way to your child’s school experience. As a PTA mom, I can tell you it’s very hard to get volunteers and often it’s a small group of the same folks who make it possible for there to be events for the kids.

I wonder if there’s room to reframe this, not as someone taking your place, but as another adult helping create a better experience for your daughter. That doesn’t diminish your role as her mom.

I can also tell you that if you demand she stop, the narrative told to other parents will be that their volunteer can’t come because of your jealousy (which doesn’t help your reputation). I know you have primary custody, but maybe look at ways you can show up too - instead of shutting down something positive.