Gut feeling that ex husbands girlfriend is being unkind to my daughter.

My ex and I split up a few years ago, I’m remarried and he has had a year long girlfriend. He’s a very narcissistic man and has anger issues, he only sees the kids every two weeks and only has visitation rights. With him, our daughter is his favorite, he’s always been awful to our son and there was abuse issues in the past when we were together but only ever towards our son, he always wanted a boy but when he got him he was awful to him and the entire pregnancy. With our daughter it was the complete opposite, she’s been his princess since day one. He’s better now, the limited contact with the kids seems to work well with his anger, and he’s so concerned with showing off what a “great dad” he is now in public and on social media that he seems to behave himself around them now. That was a little back story, so I’ve always liked his girlfriend. She’s kind of a traveling nomad that doesn’t want kids of her own and is perfectly happy leaving and doing her own thing and then sometimes spending time with the kids. Well his parents have put a lot of pressure on her to be more of a “mom”, which to me she is who she is, they have a mom and if she just wants to casually be around them but not be a mom figure I’m fine with that. Recently, I’ve noticed my daughter (she’s 4) has been more upset in regards to the girl friend. When I ask if they had a fun weekend she gets sad and will say Anna wasn’t happy with her, or Anna wasn’t nice, or recently my daughter said she picked up “adult” scissors that were on the table, she said anna got mad and spanked her, but my 4 year old didn’t know what she did wrong, and for some reason this specific scenario really bothered her, she kept saying “I didn’t do anything wrong, I just picked them up and Anna got mad and spanked me.” Which I wasn’t there for this, but the scenario to me didn’t warrant a spanking, I think it also hit a nerve because we never discussed girlfriends physically punishing the kids. Even their step father tried not to use physical punishment out of respect to their father and we thoroughly discussed what disciplines my ex was comfortable with their step father doing so we didn’t cross a line. Anyways a few weekends ago and the kids soccer, they were drawing in the dirt with sticks (both my son and daughter) and Anna went up and was ripping the stick out of my daughters hand, I didn’t hear or see anything the kids were doing wrong, I just heard my daughter crying and saw Anna pulling the stick away but didn’t say anything to my son who was doing the same thing. When Anna came over I asked what happened, I said I didn’t see what they were doing, and she mumbled something about hating when kids kick up dust… these kids were far away from people in their own little dirt patch and I never saw them kicking up dirt. It rubbed me the wrong way but I left it alone. But between witnessing that and hearing recent things from my daughter I worry about how the girlfriend treats her. If since she is her dads favorite if the girlfriend might be treating her unfairly because of that? My kids are well behaved, well structured and they know they have expectations for their behavior. They aren’t perfect, but my gut is saying something isn’t right between the two.

How would you go about handling this situation? Talking to the dad won’t do much, he can do no wrong in his eyes and his father laughed in my face last weekend when he son couldn’t even bother to tell us that he wasn’t bringing my daughter to her soccer game after we had already been there for 30 minutes before her game waiting, so going to his parents will be a waste of time. I don’t know what to do here. My sons no help either, his dad has told him time and time again not to “tattle” and tell me what goes on. When he does slip he catches himself and completely changes or or talks over his sister when she tries to tell me something that happened.