First Gynecologist Appt for a girl with PTSD

I'll be 18 in about two months and my mom FINALLY decided it's a good idea to get me into the gynecologist. I have an appt tomorrow. I'm really scared to go in because when I was young I was sexually abused often. I have PTSD and I'm really scared of something setting me off in there. 
Does anyone have advice for me? I'm desperate.