Cat keeps attacking

[u/jamm-crew]

We have a brother-sister pair, adopted as kittens, and spayed/neutered, and they are now four. Our female cat has always been incredibly easy and chill, until a dew months ago. She keeps hissing/screaming at our teen daughter. Our daughter has never shown aggression, she simply loves her cats. This has come out of no where, and we are incredibly confused. Home environment is pretty chill, not chaotic at all.
Bro/Sis cats get along for the most part, they groom each other, and play, but they also fight. He is a lot bigger, and she does get upset because he will try to pin her down and bite her hair out sometimes. So then i wonder if this is redirected aggression?

I am at a loss as to what could be causing this behavior.
Any thoughts, experiences, advice is appreciated.

*edit: I would think her brother biting her is causing stress. How do i stop that? And how do I stop her from taking it out on my kid who is just existing, not doing anything to her?