https://en.wikipedia.org/wiki/Angel_wing
There are lots of theories about why it happens. . I don't think anyone knows definitively why it happens. Sometimes one bird who is being fed the same as all the others will get it while the others do not.
My opinion leans towards a combination of a...
https://www.backyardchickens.com/threads/angel-wing-treatment.1252014/
I would give her niacin just in case, but sometimes they just sort of sprain their hip and limp for a few days. Hopefully it's nothing serious.
I wouldn't bother trying to wrap for the angel wing personally until she molts...