Hi Shane, my daughter is a 14 year old catcher. She also typically holds her hand in a fist behind her glove for a quicker transfer. She used to (and occasionally still will) hold her hand down by the side of her leg. The most important thing, though, is either way make sure that she is not starting to hang her hand out to the side of her glove prior to the pitch actually being in her glove. This increases the risk of injuries to her throwing hand/fingers by a late foul ball or a pitch that does something crazy at the end that she doesn't expect - she and her pitcher are on the younger side, this happens sometimes.
When my daughter's catching coach first started having her do the fist behind the glove (at about the same age as your daugher), she had a habit of hanging that hand out. We broke the habit with the help of the lacing on her catcher's mitt. Her mitt at that time had lacing that came around and tied low on the back side. We had her hold on to those laces until she felt the ball in her glove. It's funny now because I have so many pictures of her from back then playing with the laces prior to the pitch. Having her do that might have slowed down the transfer a tiny bit at the time, but it helped her learn to keep her hand protected. The catcher's mitt we bought 2 years ago doesn't have the laces there to play with. At first she had a hard time getting used to not having them,
but it's worked out well in the long run and she keeps her hand safe most of the time.
