Okay we are back and have some answers, although I don't know how this is going to pan out...
Cookie's teeth are double checked and fine, however the x-ray and examination has shown two things, a slight bit of Arthritis in the jaw and the main issue which is located at the back of the jaw bone where it will meet the skull - she has an overgrowth of bone which we could see clearly on the side xray that is catching and causing issues when Cookie is opening and closing her mouth. On a healthy guinea pig this bone spur is not to be seen.
Rosie has seen this once or twice before in older piggies, She said sometimes the body corrects itself and piggies start eating again in weeks by finding ways of chewing not to cause the pain without any surgical intervention, other times she has done a small operation to make an incision and file the stump down (sometimes it can grow back) But she'd want to see if Cookie would adapt first..
She has had a shot to stimulate her appetite and will be on a higher dose of metacam until Monday, If she is still not eating better she will have steroids to act as anti inflammatory, switch pain relief to opiate to see if that does anything to tide her over and she begins to try to eat. We have decided on the operation towards the end of next week if Cookie is still struggling.