Looks like possible dry fowl pox to me, too. It could be a secondary problem associated with whatever is wrong with her, or the main problem that is weakening her. I would isolate the sick hen in a warm, clean place where you can observe her. Offer quality chicken feed and whatever else she will eat (scrambled eggs, mealworms, various fruits, etc.), and put some vitamins in her water if possible. You can also put antibiotic ointment on the scabs on her comb, if you want. I would also recommend giving her an antibiotic (like Tylan50 or oxytetracycline) to treat any secondary infections brought on by the stress of the (possible) fowl pox.
Is her crop squishy or enlarged? If so, then she could have sour crop and you're doing the right thing by draining her crop. If her crop seems pretty normal, though, I would stop draining her crop, since it is stressful and in that case, unnecessary.
I would also consider the possibility that she is egg bound or internally laying. You might consider palpating her externally (just squeeze around her body/abdomen looking for abnormal lumps) or feeling around inside her vent with a gloved, lubricated finger. At this point, though, recovery from egg binding would be pretty unlikely, since the egg (if present) would have been stuck and decaying in her body for a few weeks.
