Where does your husband stand in all this? What's his say? If his not standing up to his mother and backing you up then it doesn't help the situation much.. have you talked to him about his mom
None of this sounds acceptable. Firstly, taking the baby while you're sleeping and not informing you I would actually classify as kidnapping. I would have hit the roof over that. Fundamentally, your partner should be the one advocating for you and your daughter as it's his parents. Regarding Santa - I'd ask your partner to tell her that you will be organising to meet Santa with her (if you actually want to) and that you're busy the weekend they've booked. If they want to do something with her, then they should check with you before booking and wasting their money. Your partner needs to remind her that's she's your baby, not hers x
I would just straight up say, I'm her mother not you so I will be the one to do the santa visit. If you're away that's not my responsibility to plan her trips around you and if this continues (give examples of the boundaries and what has been broken) you will not see her until this behaviour changes. I can't stand when people tell parents what to do and to take your daughter when you're asleep, I would go mental.
Sounds like shes not communicating things very well and I can't speak for her intentions but it comes across a bit disrespectful. I'd definitely want to change that dynamic quick! It should be your husband that handles these things firmly and makes sure it comes across as a message from him and not something you've asked him to do. But failing that, I always feel like it's best to kill them with kindness. So in a really nice way I'd try and say its lovely that they want to take her out to see Santa and you love how involved they want to be in her life and all the moments they're building with her but for you seeing Santa for the first time is a special thing you'd like to do as a little family of 3 this year. There will be other things that come up like this so if she could let you know in advance that would be great and you're more than happy if not welcoming of them taking her later in the year so you will let them know when you and your husband have been and they can arrange a date for after that.
I understand she wants to spend time with her but honestly I’d have a problem too if it’s this much. In the end, It’s your daughter and you show her it’s unacceptable to just take her anywhere without asking you first. You’re not being dramatic, maybe speak to her openly about this again and be clear to inform in advance before planning anything. It’s up to you whether you’re comfortable sending her or not. :)