Forgotten Title Ancient China BG novel

Forgot the plot. Only remember a particular scene- something about fl jumping into (probably freezing) lake to save a boy(i think this occured at night. Some festival was probably taking place). ML(some Prince) calls her out for acting out with hidden intentions(cuz she wanted to act virtuous? idk). ml proceeds to bring fl into his residence to get treated as she falls ill. Please help.

 

Greetings, Ninth Uncle
The only novel I could think of. It's the scene before the leads get married.

 

Thank you!