How old is his daughter? If she is old enough, I wonder if having an honest conversation directly with her would help? Depending on how old she is?

It does seem like she is having some struggles with accepting dad's new girlfriend being around. She may feel in competition for dad's attention with you, like suggested above, and she may fear or worry that you are trying to take her mother's place.

It's a very difficult position to be in, after a couple divorces and when you're interacting with and trying to have a relationship with a child of that divorce. There's so many different emotions involved for that child. It's very hard on a child, especially when they're young.

It may even be better if her father, your bf, has a conversation with his daughter, and maybe that's more appropriate. He could explain that you're not taking the place of her mother, that you are special and important to him, but that she herself, is also most important to him... in fact, it may help MORE if HE talks to his daughter.

Can you ask him to do that?