I don’t think the vet knows what he’s talking about if her crop is full and hard, and never empties less than the size of a baseball. She may have a pendulous crop, where the crop muscle is overstretched and has lost its tone. Azygous has a good article about crops, and that is what I would do...
If her crop is huge and hard, and not emptying, that is an impacted crop. Does she crop ever empty by early morning? She needs poultry grit to help digest foods other than chicken crumbles or pellets.