In our dojo, I have no idea whether the ladies wear a bra or not, or what type. That is really their personal preference. However, all females, regardless, wear white T-shirts under their gi top, and they also have tie straps on the front. Recently, many of the guys have been sporting these tie tops too, maybe they are secretly wearing bras underneath?
Speaking of the guys, many of them go "commando" under their gi trousers, whether they wear a hakama or not. Have tried it myself and it is quite liberating, quite practical too considering the amount of sweating we do in the summer here, but I tend to prefer a more packaged package, just have to ensure that you take a fresh pair to change into after otherwise you have to go home "commando"