Yes. I would euthanize her now. The deciding factor when I am facing when to euthanize is a chicken getting worse and not better, especially when it's this obvious what's wrong.
The reality is that her symptoms and the new symptoms of wing droop all indicate beginning of end of life organ failure.
I've had hens with similar symptoms and when they died, I opened them up and found cancer everywhere. I've even posted a thread...
The hardness you feel could be cancer tumors in her reproductive system.
You also can't rule out being egg bound just because you've never gotten eggs from her. A non-layer can all of a sudden produce eggs for a short period. If the hen has an aging shell gland, calcium won't be produced in...