She may be experiencing internal laying. Egg yolk peritonitis and salpingitis are 2 other conditions that can be common in hens who lay soft shell eggs or have eggs break inside. They can also pass cooked egg-like material in their droppings. She may benefit from some antibiotics such as enrofloxacin (baytril) or others. A vet could prescribe the better ones.Here is some reading about those things:
I'm still fairly new to chickens.
I think it could be related to a possible internal laying problem. You may want to Google "false layer syndrome" and look for the Merck Vet. manual link. I had a cuckoo marans once who went into the nest box almost daily, sat for an hour, and came out without laying an egg. I never knew why, but I figure that she had that.
Well, internal laying does not have a good outcome. But I'm not a vet, and a vet could probably do Xrays to confirm the diagnosis. The main thing is to try what you can to keep her comfortable, perhaps try some antibiotics that may prolong her life. But she may not have that. With chickens a lot of it is guesswork and we sometimes have to do a necropsy after they die to really find out what their problems are. Reading about the diseases is the best thing to do. There are a lot of threads or posts by speckledhen who knows a lot about internal laying problems.