I'm sorry to hear that she died:hugs
The only way to get more info would be to have a necropsy, either through your state vet or you do your own informal one.
The lice won't help.
Likely she has something else going on like a reproductive problem, but what you want to do it address any issues or symptoms that you can treat, then see how it goes.
Like getting rid of the lice.
Making sure her crop is emptying, if it's not then begin treatment.
Get...
Re-check her crop again first thing in the morning, make sure it's empty/flat.
I'd work on getting some dust or spray and treating all the birds for lice.
What do you mean the crop feels empty but doughy? So it has something in there right?
I would treat for a doughy crop or at least start giving her coconut oil twice a day an massage the crop.
Sounds like you may have found some bugs. Permethrin poultry dust or spray can be used to treat...
I agree, I would re-check her crop in the morning.
With this going on so long, likely she's not egg bound, but she may be having some reproductive problems.