Sorry it's taken so long for someone to respond. Maybe no one knows. I for sure don't but here are a couple of guesses. She does need grit to digest. Put some parakeet gravel in her food. I use that when I have baby chicks off the ground and confined when very young. Also. I find that a bird/chicken/duck often is effected with some lameness when fed too high a protein diet.... The yogurt, eggs and such are very high protein.... try canned veg. green beans, some corn, carrots , pinto beans etc. soft, and low protein. When my ducks come down with lameness from getting sweet feed from the horses, I confine them and give them shredded carrots until the recover. Sounds like Abbey does want to make it. Is it possible to put her next to her true love or maybe with him. He might encourage her. Also, don't know if your are inclined but this time of the year I'm often found in the mater patch picking off mater worms for my chickens. They are fools for the ugly things. Just mention that because insects,worms are a natural diet and Abbey may benefit from bugs.
Now I see Abbey's mom fliting around the yard with a net looking for some bugs for Abbey? Abbey is a lucky chick/girl.