Angry Mom is a drama and She's on Duty is a movie, but they both have driven female leads who go undercover as a high school student.

Both movies have a strong female lead who is good at beating/killing people and has a mysterious past.

My Bratty Princess doesn't have the time travel, but gives the same sort of feel and has the unruly princess.

They both have: smart female protagonists who dress up as men in the beginning of the story; intricate planning and court intrigue as they battle their way to the top; multiple love interests; etc.
Empress Ki is a much better fighter than Queen Seon Duk as an individual, but Seon Duk was up against a more intelligent foe and had some brilliant planning.