Daughter wants to be a boy

So my daughter wrote me a note ( because she has a hard time talking out loud about deep emotions) and said she wants to be a boy. She already knows she is a lesbian and regardless we will always support her. I am just trying to get an idea of what we can do to help her. We want her to be comfortable with who she is but she is too young for a sex change. So how do we help her until she is able to fully change to what she wants? Any suggestions/advice for a parent in this situation? Thanks in advance!