I’m very sorry to hear about your cockatiel but I’m afraid if you do not seek Vet care as soon as possible, she probably won’t survive. Splayed legs need to be treated very early, so it’s hard to say if anything can be done for them now. Unfortunately, if badly splayed, the bird can end up with organ damage from being on the chest and belly all of the time. And sometimes splayed chicks have internal issues, because splayed legs can be caused by genetic issues or poor nutrition for the parents. But she could just have something simple like a bacterial infection that can be easily treated by the Vet. If this chick came from a pair you own, I wouldn’t breed that pair anymore. As for the poor chick, again, Vet care is what she needs.