Actually the girl didn’t drag them into anything, the cousin (bully) did the moment he recruited ‘crown prince’ to fight his battles. Gilsu wanted to get back at the trio for essentially disrupting whatever crime plans he had going on by being entangled with ‘crown prince’ and the other kids that might be apart of the scammer ring under gilsu. The girl only tried to help give the trio an advantage to counteract gilsu by trying to give them better chances of putting him prison. Because if they tried to do that on their own without any proof or information on gilsu and his ties they could fail and forever have a target on their backs by gilsu. Plus, gilsu could easily kill the girl if she tried to do everything on her own and failed. Because remember, he kills for money and will even severely injure anyone just for crossing the line. So she essentially didn’t have everyone else do the dirty work. She helped them try to help her to get gilsu in prison.