Doesn´t she start off with Typhlosion and Ninetails instead of Darmantian? At least in episode 13 it was like this. Didn´t even have one. Not sure if Ame changed it.
Getting a Pokemon with Rain Dance would be helpful as it would in combination with Sunny Day create the Rainbow field although Hidden Power could still hurt you. If you have a fast Pokemon (or one with Prankster) and you have the Rain Dance TM, I would use it.