You can try working with her lifting her to judge if she is getting better or worse. The sling won’t do too much to make her walk, but if she has an injury, that might help her rest her legs to heal. At 5 months old if she was not vaccinated for Mareks, I would be a little suspicious about that. Mareks cause imbalance and may cause lameness in one or both legs, or dropping wings. It can best be diagnosed with a necropsy by your state vet if you lose her or decide to put her down.