However, all this was just to make use of the time you need to wait for your opponent to get a 30-combo counter. To keep the combo counter alive whilst you transition between barrels, I suggest equipping her shotgun and abusing the Quick Shot ability quite a bit. Then, use gather all the enemies around the two explosive barrels that you start near, one explosive barrel at a time.
I find that an easy way to kill enemies and overload an opponent is to create a match for Rail Yard, playing as Helena (I had 'Go for Broke!' skill equipped, but you might prefer something else).
