Well she did spend the time between Season 1 and 2 and a fair chunk of Season 2 training with May so yes, she's also a badass fighter.
As for using her powers Vs a gun. Well the two times she used them in the episode she had time to prepare. Also we don't know if she's slotted for endurance and recharge yet. Those guys came in quickly, in small groups, from several directions. If fighting with a gun is now muscle memory it may simply be easier rather than using the new thing.
Plus she couldn't help showing off to Ward, as a warning.