At age eight, she may have an underlying issue that's slowing down the crop and making her lethargic. it's impossible to diagnose, but there's a decent chance it's cancer in the reproductive tract. When crop issues persist after trying all you have done, it often boils down to cancer. The only way to know for sure is to open her up after she dies and look for tumors. They are very obvious and you don't need an expensive necropsy to tell you what they are. I had a hen like yours. She died and I found what looked like bean soup in her abdominal cavity, she was so riddled with cancer tumors.