the FL is just being an asshole and bully and since mentally she is an adult this makes it even worse but most people won't see it that way since most people at least to me when reading manga/webtoon tend to turn their brain and morals off and let their biasness get in their way of being logical
She did thought/think that due to him act immature she also act immature.
As her body lack the frontal lobe of the brain so is more prone to acting immature despite all the life experiences.
[Her body and physical brain is not adult yet, so lacks logical thinking and processing.]
(I believe if around adults or family = mature, around people her age = more immature at times) especially people that annoy her? Maybe?
