I don't know. She may be safer with just the combustible cloud.
A poison cloud is tricky cause, for one thing, how do we know it'll effect them? And then there's the fact that these things are invading a town, and it's kinda hard to control the area of a poison cloud. It only has to skim the edges and the defenders will be hit too, and you can't just drop into the middle of the swarm and distribute it, cause they'll tear her and whoever is there to pieces.
Fire is good, cause nothing normal likes fire, they could be herded quite effectively with it, especially if Bolt's guy can control the winds. I'd create an outline of a semi circle of fire in front of their herd, two fighters behind it to take care of anything crazy enough to jump through, the others would be at the end of the curved line, to stop any of them flowing out, and the poison is sent through, should be simple thanks to, yet again, control of the winds. Let them run towards you, set off the fire and they'll be shoved into it by their own momentum, the ones that are forced through would be easily picked off by the defenders I imagine. And the poison cloud would weaken the bastards before they enter the fire and kill off most of them if they get around it.
Heck, you don't even really need to kill them all. You just need to kick the stuffing out of them so the defenders can take care of the rest. They could probably handle 50 or something, especially if those 50 don't come in one go, or are poisoned, or are burned.
I'm not sure if I made it clear, or if there are flaws, but I hope there're some things that could be taken on board here.
-"I'm sophisticated, charming, suave, and debonair, Professor. But I have never claimed to be civilized."