As a child the Wretched Egg destroyed the majority of Tokyo with a 11.4 Earthquake. I've heard it calced to 1.9 tetratons. She survived this as well as it was a deliberate effort to kill herself. When she got older she could generate earthquakes like this casually(the destruction limited because of the Mother Goose System). She is far and away the strongest thing in the Deadman Wonderland setting and only "loses" because she wants to die.
All this to say, if Ryuko and Satsuki can deal with that kind of power and generate enough power to kill the Wretched Egg, then they should win. Simple as that. I dunno Kill La Kill.