Why is Scout so surprise when Jen says, "It's time you started bein' a girl and acting right? What is Lee's purpose for having Jem say this?

Jem had never questioned Scout's "tomboy-like" personality. By chapter 12 Jem has hit his middle-school years. Scout finds Jem moody, angry and prone to long silences. What horrifies Scout the most is when Jem tells her to "act more like a girl". Jem is maturing into a young man with all the questions, confusion and chaos that goes with adolescence. Scout asks Calpurnia if she might be able to fix Jem by beating him up. Cal and Atticus tell Scout to give him some space. I think Jem is not only feeling the changes in his body, he is also grappling with issues that plague his father and his town. Issues of race, values and human nature seem to be hitting Jem almost at once. He needs time to comprehend it all.