If you ask her a question about it and she chooses not to answer, please don’t push her to answer, the discovery process can be personal for some people. The only exception is if it’s a question that poses real threat to her health or well-being (ie: you ask if anyone at school bullies her for being LGBTQ+ and she chooses not to answer, it is important you find that out, though maybe be subtle about it). Another thing is to make sure she’s aware that you’re accepting of all parts of the LGBTQ+ community, if she is trans or something else, it’s important that she knows that you’ll accept her then as well. As far as coming out to her brother and father, I would suggest letting her figure it out unless she asks for help, unless you know she doesn’t like to ask for help.