Uniform Stealing Board

The heroine bumps into an evil female doctor (dressed in regal clothes as befitting the era of ancient China, we assume) and tails her to her private quarters. She initially plans to kill the woman, but decides instead simply to tie her up and replace her (though using a different outfit to disguise herself, for some reason).

First encounter at 4:40. Scene starts at 6:00. Discovery at 14:55.

https://www.youtube.com/watch?v=JXmC3CS3kvk