There are three evidences: 1. Kong Wu asked if the handkerchief belonged to Qian An, but Qian An said no.
Rufei immediately returned the handkerchief to Kong Wu, but in the last episode, she could read the word on the tower.
3. The interview with Deng Cuiwen, the actor who plays Rufei, and the producer (equivalent to the director) of this drama after the broadcast also said that the handkerchief is Rufei.
In fact, I think if Rufei had told me earlier that the handkerchief was hers, there would be no aunt Anxi behind.
Please pay attention to War and Beauty 2, which has been produced in the later stage.