One of our instructors was a female with an un-Barbie like body, it made no difference to us! She was very good at instructing and obviously a proficient diver, so... (what difference does it make?)
On the other hand, the female vs male teaching style... I think we got the best of both worlds there. The male instructor cut to the chase "You're doing that wrong, see -do it like this or you'll get in trouble when you..." (You get the point.) The female instructor was more about encouragement and taking time to explain things more fully. The two different styles worked well -some students gravitated to the male instructor, the others to the female. The interesting thing was that it wasn't necessarily the women who needed the encouragement and what some might call "hand holding". -There's such a wide variety of student divers out there, that all kinds of (good) instructors are needed. Some will like your style, some won't.
...and let's not forget female students. Perhaps they'll feel less intimidated by a woman teacher who's not Barbie? -I have a friend who looks like a Playboy model. She intimidates the heck out of the women around her, and while the males are attracted to her, their wives forbid them to even speak to her. -It's not easy for "Barbie" either!
Student divers are looking for good instruction -that's the bottom line. Most of the students in my class were in their 20's or 30's -far beyond high school age where 'looks are everything'. We were all looking for the best instruction possible. Relax, be yourself, and concentrate on being a good instructor. No one cares what you look like.
DISCLAIMER: As a female who's generally considered a tomboy, I understand that I'm stereotyping the male/female roles above. I'm speaking in generalities here...