I think the 12u/14u aspect is being looked at way too hard. Sure there is an age gap but they are playing ball not becoming roommates. Instead of looking at it like a potential problem look at it as a chance for her to gain maturity and experience.
I cannot repeat some of the things I have heard second-year 14U girls say to each other in dugouts. Some of their conversations can be truly shocking.
All I do is coach 12U and 14U over and over again. With that experience, I greatly prefer to have 12-year-olds stay away from being exposed to it as long as possible.