I'm glad this is all working out for you and Coco, she is adorable...and shouldn't have any issues getting around at all with the splayed legs...
On another note, not to get any money back, but to save any other babies from being permanently disabled, I would highly suggest calling the breeder up simply to tell him that your baby came home to you that night with a horrible case of splayed legs, which is caused by him not properly lining the nest boxes with bedding, and that she didn't have any idea how to perch, which is from not switching his babies from nest boxes to weaning cages when they start to pick at solid food. If one baby has splayed legs then they all likely do, and if he has 30 birds that means he's breeding all kinds of babies will issues. He may not know that he's doing anything wrong, or he may know and he doesn't care, but just in-case, I'd drop him at least an email telling him about the splayed legs and the need for immediate vet care, splints, and still Coco is permanently disabled, and that he needs to do research on how he houses his babies from nest box to weaning cages to prevent this from happening anymore...poor babies..
Green Cheeks are very loving, cuddly birds, and I'm sure in-time Coco will warm right up to you and your family. Just have to work with her daily and slowly. My Green Cheek, Bowie, is my special little baby, he is just the sweetest, gentlest, most loving little parrot I've even had the pleasure of inviting into my family. I hope that Coco brings you and your family the same kind of joy!