through a quick google search I've found "
Crop impaction and stasis
These are fatal conditions if untreated and the sooner they are picked up, the better the outcome is likely to be. Crop stasis is also called ‘sour crop’ because of the smell that goes with it – if you smell an affected chicken’s breath, it will smell something like sour milk or yoghurt. Often owners don’t realize that their chicken isn’t eating because the crop always seems to be full. Indeed, the crop continues to grow if the chicken is still trying to eat but nothing is getting through! If your chicken is suffering from crop stasis, it is also very likely to be suffering from something else: crop stasis is rarely a primary problem but is a result of other disease processes. If your chicken has a crop impaction, the crop will continue to grow as your pet eats, becoming very hot, red and heavy – so much so that it can be difficult for your chicken to stand. These problems demonstrate why it is so important to feel the keel and surrounding muscles regularly: these chickens will be starving with a full crop. Whilst you are watching your chickens eat, take the time to check that they are actually eating the grains, not just pecking around in the dirt! The only effective treatment is surgery for these cases, although medical management can be attempted if a crop stasis is caught early and before an impaction builds up. " from what you've said this sounds accurate, you best take your hen to a vet.