what caused Scout to change her mind about being a lady

Scout never really wanted to be a lady. Despite Aunt Alexandra's consistent attempts at Southern belle indoctrination, Scout decides that being a "lady" was not what she had to do Scout could see alternatives,

"I was more at home in my father's world... there was something about them that I instinctively liked... " Ch 24

Scout also had Ms. Maudie as an example of a lady with the sensibilities of her father.