It could be slipped tendon, hard to know. There are leg bone deformities that can cause the legs to bow too - Valgus Varus, with leg bone deformities, there's no fixing them.
If you can feel the tendon and it is indeed slipping out and causing the leg to bow, you can try splinting to see if...
Cute Chick!
Is there any swelling of the joint?
I'd start her on 1/4 tablet B-Complex daily and see if that helps.
You may find the info below helpful as well.
https://web.archive.org/web/20220528135316/http://www.poultrypedia.com/poultry-podiatry