Gynecologist questions?

So my mom is taking me to the gyno soon, and I haven't told her yet but I am sexually active (please nobody tell me that I have to tell her. We just don't have that kind of relationship) and I wanted to know of she HAS to be in the room during the whole appointment, and what happens if I just lie and tell the doctor that I'm not sexually active so that way she doesn't know? And what if the doctor somehow find out? Can he tell her?