If I argue that she's a girl, she becomes so upset that she bursts into tears. I point out that girls can too, but that doesn't satisfy her. In the preschool years, children are just beginning to discover what gender means. They carefully observe who's a boy, who's a girl, how they dress, what they do and how they are treated. Children's understanding and expectations about gender are influenced more by what they see and experience than what they are told.
Actions speak louder than words.
This is how both boys and girls learn about all the possibilities that are open to them in today's world. Seek out books or videos that feature girls and women in strong, active, adventurous roles. Then, since young children love dramatic play, act out some of the stories together, with your daughter in the starring role. This has the added bonus of stimulating your daughter's language, memory and creative expression. Join with your daughter in the lively outdoor games and activities she thinks are limited to boys.