YANBU however from experience watch your back.
We had a situation with a pushy mum, she volunteered in school regularly and knew lots of the staff. She acted like she was staff herself.
DD told me that during a class activity where this woman was volunteering, a group including DD were taken back to the classroom to do some reading. The volunteer mum escorted DD and two others back. Apparently, DD and her friend were laughing. This woman shouted at them both and DD was really unsettled and cried. At which point DD said she grabbed her wrist and pulled her along the corridor.
Now, no other adults saw this but DDs friend told her mum too. I spoke to the school who said they would ensure DD wasn't alone with the volunteer again and that they would speak to her directly about it.
Queue sudden filthy death stares amongst her little group of mums. I could take that on the chin quite happily. What I was less inclined to put up with was two teachers and a classroom assistant openly sneering at me. DDs teacher actually berated me about how I had "upset" the volunteer mum and she was baffled as "all the staff are" of why DD would "lie" about her. I tried to explain that it wasn't just DD and that another child had been upset and told her mum and she said "yes but her mum doesn't come and demand the volunteer is sacked and banned from being around children".
This wasn't what I said at all. But that was what the volunteer told anyone who was happy enough to side with her BS.
If this mum in your situation is matey with classroom staff, watch what you do next. Because trust me I had 3 years of sneering, tattle and gossip. DD stopped being invited to lots of things and we were genuinely treated like scumbags. And she was the one in the wrong!