Aunt Alexandra is concerned that Scout is not ladylike.
Aunt Alexandra wants Scout to be more lady-like and thinks that as she is a Finch, she should start acting as such.
Aunt Alexandra belongs to a good family and that is very relevnat to her, so that she considers that anyone who carries the family name should act a certain way.
Aunt Alexandra does not approve of much that Scout does. Indeed, she hates the way she dresses, and is reluctant accept that Atticus allows her to curse. Besides, she disapproves of her friends.