I'm 31 and I have always, for as long as I can remember, pulled out my eyelashes and eyebrows. It started right around her age and, for me, it is a very UNCONSIOUS stress reliever. Obviously, I know I do it, but I don't process it AS I'm doing it. There have been periods, some years, where I have had the fullest, lushest, eyelashes and eyebrows. They were years when I didn't have a husband, kids, full time school, ect. Even when I am not stressed it can sometimes be a calming effect, similar to the infant that strokes mom's hair to fall asleep.
Now, I have never been to a dr but I am pretty sure I am not bipolar so I don't know anything about meds to help.
It is a deeply ingrained habit and will take a lot of work and love to stop. I agree with GrandmaT in that it is alot like biting nails. At her age, I don't know how you can call her attention to it without making a big deal out of it or making her unhealthily self consious about it. I know that when my husband mentions it to me now, I get defensive and it gets worse.
I'm sorry. I'm rambling. I dont' really have any advice but just wanted you to know your daughter is not alone.