Slipped tendon is sometimes fixed if they are very young, and some have fixed it if it has happened later on, but the success rate is fairly low. I have never had a chick with it, thank goodness. Many try to let the chickens live and see how it goes, treating with vitamins and mineral...
Welcome to BYC. Sorry about your pullet, but she sounds like she either has a vitamin/mineral deficiency such as rickets or possibly a bone or tendon issue that she was born with (many times due to deficiencies in the parent stock.) Would it be possible to post a picture of her standing...