Premarin is what is known as a conjugated estrogen. Estrogens are usually used to treat menopause or to provide estrogen to women whose ovaries have been removed. Estrogens affect many areas of the body. They DO cause growth and development of the sexual organs. Which is probably why they prescribed it....to help her development along so the labia would no longer be fused. Estrogens also help maintain female sexual characteristics, such as hips/breasts, pubic hair and armpit hair. They also increase cervical secretions (which helps menopausal women when they are "dry") and growth of the uterine lining. When they prescribed this medication to your baby, they should have informed you of the potential side effects. I would say that it is almost definitely expected that she was going to develop pubic hair as a result of this medication. And if she were older, maybe even 8 or so, I may have expected even more than that, like possibly development of breasts and such.
I'm sorry that you are dealing with this. I wouldn't sweat it though. Since you used it for such a short amount of time, it probably only caused the growth of pubic hair and not much else. Did it at least correct the fused labia? Well, I hope that you get some answers from the endocrinologist. Good luck to you and your baby girl.
K-
If the medication had any form of steroids in it its possible that had a lot to do with it. The hair didn't appear until you discontinued use of the cream which could of been a side effect of the abrupt stopping instead of lowering the dose little by little. This may be a fact you want to bring up to the endocrinologist.