What are her droppings like? If her crop keeps filling up, and she is getting skinny, one thought is that she has an impacted gizzard. Unfortunately, there is no good treatment for that: all you can do is try giving her some olive oil and see if the blockage breaks up.
Of course, it is still possible that her problem is just sour crop, so don't give up yet. One treatment that works for some birds with sour crop is using an anti-fungal medication, like Monistat. Other things to do is give her plenty of probiotics, and keep emptying her crop.
Other than that, though, I'm not sure what else you could do. I don't have personal experience with a major sour crop. I did have one hen who was prone to the problem, but her cases always cleared up with a few days of extra probiotics. Hopefully, someone who is more knowledgeable about sour crop comes along and helps you.