Cassie pushed Nico ahead of her onto the building -- if the other girl fell (not likely, but it didn't hurt to be safe), she'd be able to catch her without blowing their cover with the power of flight.

"Don't look down!" she sing-songed, taking a moment to hike her skirt up above her knees in two handfuls of fabric which she passed back between her legs and then wrapped around to the front again where she tied them together in a knot. It gave Nico and Raph a chance to get climbing, plus there was no way she was going to spend the entire climb stepping on her own skirt.