Ah whoops. My bad. I took it as "the 2nd map that drops Charlotte", which would be the 70/6 map. If it's the other one, then yeah, it's 25-27%.
@Kirito Rick - In case if you didn't know this, but all event maps on DMM get 100% drops the first time around. And then they will return to their original drop rates for any attempts after that. Makes it easier for farm events, since you are guaranteed 5 copies of the farm unit.