What are you calling "shell grit" - oyster shell? That's great for adding supplemental calcium but it's not hard enough to act a grit in the gizzard.
She can have her normal pellet or crumble poultry feed (wet or dry) and easy to process food like the egg you gave. I would avoid whole grain, seeds, etc. until the crop issue is resolved.
Lice generally is not something that would cause the crop symptoms, but I suppose if the infestation is severe and her system is that compromised, they lice could be part of the problem.