I'm finding it really interesting tbh!
And I'm examining why I responded.
I even spoke to my adult daughter today who is doing an MA in a branch of sociology.
She thinks that female grooming is deeply personal. We're flooded with messages about it from a very young age, and how we respond to those messages says a lot about us, but unless you tell people why you're doing something they'll never know. So OP could be deeply in thrall to the patriarchy and desperate to look pretty. Or she could not give a flying fig and be saying FU, I want to do this and I will! Noone will ever know by watching her take her mirror and applying makeup in public. It's her choice.
Equally, you have no idea how the woman who responded feels about it🤷 her values, her fears, her need to be who she is. What other actions the op does that influence her opinion.
So really neither is being unreasonable, but equally both are. They've both made a very private choice and chosen to make it public. And that's ultimately up to them, but both of them have to accept that if they make their choices public and outside the norm (again, I've never noticed anyone applying makeup at lunch time before, but equally I've never seen anyone blatantly take the piss out of someone who would either) then people will comment.
And OP posted on a public forum. No one told her she was vain. She inferred that herself. There could be multiple reasons the other woman is mocking her.
I don't really think anyone is wrong or unreasonable in this case. It's just a bit of a personality clash.
And yes, it is deeply sad that I have spent all day thinking about this, but I'm supposed to be doing council tax rebate paperwork and it's really boring.