She's on Duty (Korean Movie)

Description: Detective Chun Jae In thinks that she is about to break a huge child prostitution ring, but when she finds that she has really ruined a much higher-level undercover operation, she is embarrassed and humiliated. Despite this, an important new mission arises that requires her unique talents - i.e. her ability to dress up and convince as a school-girl. She must go undercover once again, this time in a school, under the pretence of being a new student so that she can ensure the safety of the daughter of an important Mafia witness that the police want to locate. Before long she finds her maths skills challenged, her fighting skills honed on the school bullies and her heart melted by a fellow student. But will she be able to stay focussed on the mission, capture the bad guys and save the day?