I will echo what others have said...see if she can swing a few different bats of her teammates an see what she likes the feel of. A used top-level bat in decent condition will serve her well. You might find a teammate willing to sell one of theirs. It's not uncommon for girls who have been playing for a while to have bats that they have out-grown that are still in great condition.
Also, welcome to DFP!
Also, welcome to DFP!