Well, it sucks when your friends say they "know you're a girl" but have a hard time with using "she." A lot of times people may "know" something in their head, but they don't really know it, fully and totally. That takes a while. I knew I was trans for years, and told people I preferred to be called "he" for a long time until my roommate and best friend, who is the first person to really "get it" started to enforce for me that I should be called "he." He really helped me see I needed to drop some balls, ahem excuse the pun, and let people know that's the correct way for people to refer to me and reinforcement forces people more quickly to realize it fully. Honestly, I think he got tired of me looking away and down every time close friends, and even my boyfriend, would call me "she," I mean he is the one who has to live with it :p Some people still don't get it, but some others have been turning around, and I can tell you those who do make you feel pretty great.
Hang in there