B.A.
There is a condition called trichotillomania where people pull out their hair, or eyebrows, or eyelashes, etc.; sometimes it is conscious, sometimes they do it without realizing it. It is often (but not always) related to anxiety. (Not necessarily trauma.) I would start with talking to her about whether there is anything bothering her or anything she is worried about. Coming down hard on her or telling her/insisting that it has got to stop would likely only raise her level of anxiety and make it worse, so talking to her calmly and gently would be the way to go.