The overwhelming majority of women I served with did not have short hair because they're allowed to tie it back into a bun (even those who work in close proximity to rotating machinery, with sometimes hilarious/dangerous results). I'm not sure about the Air Force, but the Navy doesn't even make women cut their hair in basic training anymore. Elaborate weaves, braids and dreadlocks are more common than butch short haircuts.
From a quick perusal of their standards, the Air Force is even more lax on long hair for female uniform standards:
GI Jane was just a movie.