Tactically speaking she should have wiped out the small fries first, leaving the actually dangerous Meltdowner for later. Like you said yourself, Mikoto's power is far more versatile and it would be a breeze to defeat an opponent without any defenses against electricity. However, despite the fact she has made a hobby out of hanging in dark alleys in the hopes of cooking fried punks, she doesn't possess the mentality of a fighter (yet). Not that I'd be really complaining as I'll rather take the cute tsundere Mikoto than a battle scarred veteran with dead eyes. But nevertheless in serious battles like this she is selling herself short.

Well, to keep things in a proper perspective, for a middle schooler she is definitely doing great simply by staying alive.