She's a little baby
You're coming at her with a thing with teeth on it that's almost as big as she is ... of course she's going to bite it
But you have to be able to brush your dog
Suggestions
Get her used to having the brush around ... every once in a while
just bring it out and let her see it and sniff it
when you want to brush her bring out a chewy that will have her perfect attention and while she is going at it brush her lightly .... lightly at first
if she is matted don't pull on her hair
That will traumatize her and you can forget brushing her after that