Yun Qian doesn't care about being Xu Chang'an's teacher, otherwise she wouldn't have taught him to read in the first place.
Back then, it was Xu Chang'an who insisted on learning by himself and didn't want a formal teacher-student relationship.
Roughly speaking, the rascal harbored some "covetous" intentions towards the lady early on.
Although Yun Qian thought that even if she really were his teacher back then, it wouldn't be a big deal, since she already had the titles of Miss and Housekeeper. Adding a teacher-student relationship could be seen as a novel experience.
That's how Yun Qian thought, so when she heard Li Zhibai trying to "recruit" her, she showed no resistance, but simply told Li Zhibai to discuss it with Xu Chang'an.
Of course, Yun Qian's attitude wasn't what a normal girl would have. She never thought about what she, who knows nothing, could teach at the Sword Hall if she became a teacher there?