How old is your daughter?
She's old enough to know her own mind. The child is a wonder of nature (both my girls are) and will be who she wants to be. She's also young enough to have grown in a multi-racial, multi-cultural, accepting society in which she is open to express who she is. There will be those who will oppose her in all she does, and that is life, but she's loved and supported by the important people and that will never change.
How do you know she is a she? Did you already assign her?
She's a she because that's how she identifies right now so she's my daughter. When he identified as a he, he was my son. Who she is isn't a decision for me to make. The only thing for me to do is support my child whether a he, she or gender neutral.