Note: Spoilers for episode 18 of the anime and chapter 20 of the manga (I think).
Ayane vividly remembers the time when her sister told her the single, most important dating advice she ever received: it's better to date someone who likes you even though you really don't like them than to date someone who you really, really like but doesn't really like you.
This in itself is surprising, since her sister could hardly form complete sentences, her speech interrupted now and then by a curse, a gasp or a sob. Ayane remembers the eye liner and mascara running under her sister's eyes, the ruined coiffed hair which she admired, and she realized: no amount of makeup could make you beautiful when you're crying.
With hindsight, she realizes that she couldn't really have put much faith in that advice anyway. It was given minutes after her sister's boyfriend broke up with her through text (plain sloppy) because she allegedly texted him too much (ironic and inadequate).
She followed it anyway.
A miscalculation as it turns out. She stares at her reflection, and her eyes automatically go to the bruise on the left side of her face. The bandage doesn't really help and no amount of makeup could fix it.
As she puts on her mascara Ayane absently wonders whether its a good thing or a bad thing that she really doesn't care that he slapped her. She's more concerned with the fact that she doesn't have a foundation with a good enough coverage to conceal the discoloration.
As she puts on the first coat of lip gloss Ayane tries to remember why she dated that jerk in the first place anyway. She puts on a second coat and decides she wasn't thinking straight when she made that decision.
As she puts on her earrings Ayane thinks of the right words to say to Chizu and Sawako so that she could properly convey the perfect mix of disinterest and disgust.
She surveys her reflection one last time in the mirror and is satisfied. Her hair is perfect, her uniform is as she wants it to be and she resolves to follow better dating advice.
Perhaps she should ask Kazehaya and Sawako next time.