I noticed exactly zero difference between how easy/hard it was to clear maps before and after the Edelweisss event. If you can't clear the maps without her, you can't clear them with her either. Do the work to level/evolve your girls...no one unit will make any difference if the rest of your units suck.

This is a game we're lucky enough to be able to play for free if we want to, and they regularly give away free codes for some of the girls. It's unbecoming to demand more.