If you have a cooperative and non-combattive relationship with the X maybe you can point out the recent realities of favoritism...? Otherwise, I think all you can do here though is support your DD, and validate her feelings.
...and Mother Bear Syndrome - not a syndrome. It's nature's way of making sure our offspring survive and thrive -it's Job 1.
It would bother me too! I don't have any experience like this, but I know that pointing it out to my ex would be like "criticism" and THAT never goes over well...
It sucks when the children are hurting and we can DO nothing to make it better. Lots of hugs and cuddles and sympathy for her. She will know she is special to you.
I understand how you feel - my ex's new wife (the OW) has 3 children (so that's SIX children in their blended family) and my children are aware that her children are treated differently. It's heartbreaking when they tell me how her children receive such and such or her kids get to do xyz. It's always framed (at least, from what the kids' report) with some rationalization, ie "oh, we got tickets to do this, but unfortunately that's your mom's weekend", etc, but my kids are old enough that they're starting to connect the dots.
I listen with empathy, validate their feelings, and do everything I can to make them feel like they are the center of my world. My new husband does not have children, and we will not be having any of our own, so I hope that my home and the love and support they receive here helps.
It's a hard situation. I'm sorry.
It used to rip my sister's heart out to see her children treated so badly. But she couldn't do anything about it. Later, when the kids were old enough to have some say in it they stopped visiting. Sad. Really sad.
"We're not broken, just bent, and we can learn to love again" ~Pink
I recall DS coming home from dads saying daughter got a trampoline, he got $20.
Once DS turn about 13 I made it his decision if he wanted to see his dad. I never talked "bad" about dad.
To this day, DS, who is now 29, rarely talks to his dad, and it's been that way for many years.
I allowed DS to have whatever relationship they could have on their own. I didn't take any part of it.
MLM, kids will sort it out in the end. Mine did and he's okay with it.
I can tell you as a parent to a 9 and 6 year old that birthday parties are super important to them and they measure EVERYTHING that a sibling gets. Maybe the step-mom thinks your daughter gets two parties so she doesn't have to do as much?
Just a thought... maybe you might want to bring up a "friend" has two daughters that constantly measure everything that the other gets and you wonder if that you want to acknowledge and mitigate that dynamic ASAP? I don't know what to tell you, this is a tough one.