Hi everyone

How old are your girls ? X

My baby is 2yo and I can tell u she loves me very much but she’s also my very own bully lol so just keep that in mind that young kids could be mean sometimes

Sharing her age would be helpful. Also, does she have a relationship with her mother? Under what circumstances and when did her parents separate?
My teen son acted out when I started dating 2.5 years after his dad and I split. His father played a role in it as his father also had a very hard time with me dating and expressed it to the kids. Also, all my sons were grieving the family they were born into. It was a challenging transition, but things are better now. Although, my oldest still doesn't talk a lot to my partner. But he came to a point that he is happy that I have a partner that loves and respects me. He also is starting to see his own father's toxic behavior, so he can understand why I ended that relationship.

If she is a teen or young adult, I would recommend trying to find a common ground. Find something that she likes and meet her there for a conversation. For example, if she likes watching horror movies, invite her to watch one with you and your daughter. If she likes ice cream, take her out for some. When you feel like she is in a good mood and at peace, ask her directly how she feels about you and your daughter joining her family. Some relationships take time to build. She may also be grieving her old life, without a bonus mom and sister. These changes can be hard for some kids.

I see she is pretty young still. A 7 year old hasn't quite fully developed a conscience yet. Or it's just finishing developing around this age. There is a chance she has picked up a few things from one or more of her grown ups.
One, her opinion of you may have been influenced by her mother. Maybe consider the possibility that her mom actually said something negative about you. If that's the case, you can't do much other than continue being yourself with her until she starts to formulate her own opinion.
She could have developed a feeling of guilt for liking a woman that is not her mother.
Like you mentioned, maybe she doesn't like sharing her dad.
There are so many reasons, but at that young age, just give her time. Model healthy emotional regulation and communication in front of her as much as you can. Continue being consistent with her. Dad should check her on any extreme disrespect, but she should eventually come around when she sees you are there to stay and a good woman.