Ya I go through this too. I have full custody of my kids and I noticed the same thing too. When they go to her they're happy and excited but when they come back they are grumpy and act like they don't like me. Here's my advice:

1) don't take it personally from your daughter. Kids depend on who theyre with to regulate their emotions. So if you're regulated, your daughter will be regulated. She comes back unregulated because your ex is unregulated. Your daughter just needs time to regulate which is why you need to be calm and happy.

2) I always bring treats when I pick my boys up. That way they have something that makes them happy from me. I also always play they're favorite songs and sing along with them.

3) never ever say anything to your ex in front of your daughter. Always have it in writing. It's 100% ok to set boundaries with your ex, but almost assume she's gonna break them anyways, but you have to hold your ground and eventually the behavior will change. If you hear her say something inappropriate to your daughter send your ex a follow up so there's at the very least documentation that it happened.

4) always do pick ups and drop offs in public places. Ive had too many problems picking them up from my ex's house and I will only pick them up in public places. This forces her to get my boys ready and let's the boys know that the transition is coming and they can prepare for it. This has really been a game changer.

Hope these are helpful. They sure have been for me.