Sour crop can be a symptom of something further down, rather than a health issue on its own. So what you're doing may help, but might not be the complete answer. My Marigold had similar problems and the vet said the green poo could indicate a liver infection, which cleared up after antibiotics. Three years later, she's still entertaining me by regularly going broody.....
Green poo by itself can be the result of eating too much greenstuff, but if she's sitting looking as if she has a stomach ache, I would think she probably has. At her age she should be laying well at this time of year, so if she has stopped in the last few weeks, it sounds as if it could be something internal which has developed gradually, and the other symptoms, poo, loss of appetite and lethargy, have only recently become evident.