I have this habit.
AFAIK it's like biting your nails.
I started as a teenager, about 14. I was unhappy at the time (see teenager :o ) but there weren't any particular stresses.
TBH I think your description of a hair-twiddling habit that got out of hand is pretty accurate.
Whenever this comes up I find the attitudes to it a bit ott.
I can certainly understand why you are concerned, but I think advice about figuring out why she's doing it, as though there must be some big problem at the root of it, needlessly alarmist.
If your kid started biting their nails would people be so insistent it was anything more than a compulsive habit?
What does she say about it herself?
I pulled myself a visible bald patch once but was then able to restrict myself to parts of my head that weren't so noticeable (sides and back).
I definitely have time when I do it more, and I do it less as an adult.
Bizarrely I barely pull at all when pregnant (not suggesting this as a solution for your DD :o )
I believe the tric association is great and very useful. I've never felt the need to contact them, but I imagine it would be useful for you as the parent of a child who is doing something you can't understand.