it is because she is married
Just going by everyone else's wild speculations of everything from her being a friend of the family to Jill's mother.
None of my theories I want to add.
Reason I left the married part in there is we can draw some speculation from that.
Let's say married at 21, together long enough where she apologises to a picture for getting horny over an idiot. Hasn't had sex for 3 years and husband is either missing, left her or dead. They were obviously together for a while cohabiting so at the very least she's late 20's early 30's.
If the extreme speculation turns out to be true and she is Jill's mother she could be closer to 40.
Consider that her character model looks no older than the other students and basing off tiny bits we do know.
She would have been married at 16-18 jumping into the first relationship she was in headfirst. Husband would have left pretty soon after.
If she is still young that means we have a naive, cynical idiot that rushed into a relationship and looks down on men for whatever bullshit reason swims around her mind because "they are only after 1 thing" which she'd know with her extreme lack of experience.
So either she's older and lived enough of a life to get naturally cynical or she's younger and a naive judgemental bitch.