This is the hard part of FIRST.
Some suggestions: contact "the Society of Women Engineers" (I think it is
www.swe.org, but check) You have a huge selling point in being an all girls team.
Start asking all your parents and mentors for a contact among their friends and co-workers. Be prepared to write a professional letter stating exactly what you want. Be prepared to give a presentation on why they should sponsor you. Mention all the scholarships thru FIRST.
I have more advice but lets see what other suggestions you get.
Hang in there.