This was also a matter of necessity; while Luo Yu and Tianlan had some combat capabilities, Gita's abilities were almost entirely unrelated to combat. Yet the girl was insistent on taking part in battle along with everyone else, so Fang Hong had originally planned to have her help with operating Mr. Greyrock's Crossbow Cannon—yes, he intended to install one on each side of the platform. Of course, during the actual combat training, she would have to make do with a Magic Guided Gun for now.
Generally speaking, it was Fang Hong's responsibility to teach Gita how to use firearms. He had gained some relevant experience with firearms during his studies with Kapuka and had personally seen action with a seven-shot rifle.
Occasionally, Hilveld and Xiesta would also take up the mantle of teacher—being professional Gunslingers, the latter was certainly more professional than Fang Hong, although the Lady Noble usually didn't spend much time in the activity room.