They are all a little bit different, and that's the fun. Once while on vacation in Jamaica I spent a few hours of fun with a girl that must have been drinking a lot of that super-strong coffee they have down there, cause I swear she tasted like coffee. Not bad per-se, but definitely unusual. Who hasn't had a "reunion" with an old girlfriend after a few years and had that experience of deja-vu when you caught the first scent of her pussy again?
They change a little, but not all that much, and a lot depends on her diet. As for what it "should" smell like.....well beauty is in the eye of the beholder, right?