So, Huang Que insisted on keeping Chu Anqing in the dark about her situation...
[It wasn't about face.]
What then could it be?
Lin Xian paid attention to the details Chu Anqing had just mentioned...
First, Huang Que didn't allow Chu Anqing to call for help and told her not to seek help, but a little while later, she acted as if nothing was wrong.
That suggests she wasn't sick; she knew she didn't need help, she knew she would be fine after a short time, and that's why she stopped Chu Anqing from calling for others.
Second, she consistently prevented Chu Anqing from looking at her face, and An Qing could distinctly feel the intention behind it.
If you rule out vanity or concerns about looking gruesome, damaging one's image, which are silly reasons... the most likely reason is that Huang Que was afraid of something on her face being seen by others, or rather, there was something on her face at that time that she didn't want anyone else to know.
Last, and most importantly.