1. "I kept aloof from their more foolhardy schemes for a while, and on the pain of being called a g-irl, I spent most of the remaining twilights that summer sitting with Miss Maudie Atkinson." Here we see that Scout hated being called a girl, hated it so much that she avoided Jem and Dill altogether just to escape that "pain".
2. Just before this quote, Dill had asked her to marry him because she was "the only girl he would ever love", but then he neglected her, so she beat him up, twice. Again, we see that she enjoyed the attention of being a girl (she was proposed to because of it), but when she was rejected, she acted like a boy and beat him. A girl would have verbally accosted the rejector, or thrown an emotional tantrum-not get in an all-out fist fight with the guy. :)
3. When Jem tells her to "shut your trap or go home-I declare to the Lord you're gettin' more like a girl every day!", Scout's reaction is, "With that, I had no option but to join them." She felt like she had to prove she wasn't a girl, by "shutting her trap" and going along with a ridiculous plan to look in Boo's window. She attempts to shed her "girliness" to hang with the guys.