I wonder about that.
We do have Cultivators that are potters and craftsman; why not courtesans?
Wouldn't there logically be Cultivators that seek 'pleasurable company' that isn't as fragile and clumsy like a mortal would be in such circumstances?
*shrugs*
Reds aren't much more durable than mortals, frankly. (a newly awakened red get's all of two auto successes against mortals. A newly awakened green gets twenty one, if I understand the rules correctly.)
The simple fact of the matter is, the way the letters are composed betrays an actual ignorance about cultivators. It's not
just her confusion when it comes to zhengui. (something every cultivator would know.)
Do you recall when Qi first wrote to her regarding her nobles friends?. She warned Ling Qi about associating with nobles because of how easily they are offended.
Pretty sure she was talking from personal experience, but it also assumes that Ling Qi will not be a noble. (which she will be, soon.)
It's a bunch of little things, really.Qi mom is well educated, which suggest a decently well off background, but isn't well informed into common things that every cultivator deals with.
It's why I believe she was a mortal servant to nobility. If she was raised for it, she'd have to have at least some understanding of the ways of nobility if only to avoid offense.