any oil will do.
the crop is like a little sac near the bottom of the neck on the breast.slightly to the right..(hen's right)
the best way to check the crop, is to check it at night..
it should feel full...
then recheck in the morning before she eats..it should feel empty, or flat..shouldn't have any lumps..or grainy feeling..
is it soft and squishy?
it's possible she could have sour crop..sometimes can be treated with yogurt..or even apple cider vinegar.
med for sour crop is Nystatin..
sometimes called Medistat, Mycostatin, or Nilstat.
treats yeast infections.
http://www.foyspigeonsupplies.com
check her mouth and throat if possible, using a flashlight, look for any sores, or blister like sores..
canker can be a cause of sour crop.
have you considered she might have cocci?
cocci symptoms are watery droppings, sleepiness, lack of appetite.
try calling some vets and ask if you can have a fecal test done for worms and protozoa (cocci)..
if she has cocci..she needs treatment asap.