Well, let me break it down for you.

If Melody was in a crowded place (And for some reason visible, since she spends most of the time Carson is in public out of sight), and suddenly felt her emotions shift, she would tell Carson first since it's not an instantaneous change. Carson would probably either get out or wave his badge to get everybody to stand back far enough to be out of range, then talk Melody through it. If Carson can't get away from the people or talk her down, Melody just start pushing people back until an obvious threat showed itself. Just because she's not conscious of it doesn't make it totally indiscriminate. However, if there WAS an obvious threat (Such as someone with a knife advancing towards him, someone pushing through the crowd and touching him, or something like that) Melody would switch "stages" And kill that person, then everyone else who wasn't running away. So I guess her state is divided into two stages, Assessment and Reaction.