Urgent! Sick RIR I might have to put down soon!

I have a RIR she's a little over two years old. About 4weeks ago I noticed that she started laying tiny eggs. Then she laid a wierd shaped egg then none since. She has gotten bigger (she was always a normal size hen before this) since then too with bad diarrhea that gets stuck to her feathers below her vent. I have to soak her to wash the poop away once a week or more. I've tried giving her episom salts, yogert, and this week tried DE and she is still big and poopy. She has never done this before and all the other girls are fine. She is still getting around and eating. Some days she seems well then others she looks like she doesn't feel well. Last night she couldnt even get up on the pirch to sleep. I helped her up there. Its about two feet off the floor. I am thinking about putting her down this Saturday. I hate to do it though. Other than tumors or internal laying I'm not sure of what it could be and I would hate for her to suffer. She doesnt feel egg bound. Are there any thoughts or suggestions of what it could be or what to do?