Scout’s feelings about her gender are complicated. There are not many children her age who are also girls, and her only sibling is a boy. Jem often teases her or is frustrated by the fact that she is a girl. Although he usually spends time with her and treats her like a friend, he sometimes demeans her because of her gender.
“I swear, Scout, sometimes you act so much like a girl it’s mortifyin’.”
There was more to it than he knew, but I decided not to tell him (Chapter 4).
Of course Scout is a girl, and Jem knows that. He seems to like to pretend she is not. To Jem, being a girl is always an insult. It is not a positive thing, or a normal fact of life.
I was not so sure, but Jem told me I was being a girl, that girls always imagined things, that’s why other people hated them so, and if I started behaving like one I could just go off and find some to play with (Chapter 4).
Especially after Dill arrives, Scout spends a lot of time with Miss Maudie because Jem often insults her and calls her a girl, and Jem and Dill go off and do "boy things" together. Jem really confuses Scout when he pulls away from her as he gets older. He even stops telling her not to act like a girl, and then starts telling her to act like one!
Overnight, it seemed, Jem had acquired an alien set of values and was trying to impose them on me: several times he went so far as to tell me what to do. After one altercation when Jem hollered, “It’s time you started bein‘ a girl and acting right!” I burst into tears and fled to Calpurnia (Chapter 11).
When Scout was younger, she hated the trappings of being a girl. She preferred overalls to dresses and wanted to run around with the boys. As she got older, she learned how to properly serve at a tea party and why she shouldn’t pick fights. For Scout, part of growing up was learning what it meant to be a lady and coming to like being a lady or at least accept that she was expected to behave like one.