My little RB girl, Quasar, had a mysterious loss of appetite, too. I took her to three vets and no one could figure it out. (This was many years ago.)

They did, however, give her an appetite stimulant, which I put in her canned food every morning. She lived for many years after that and seemed to be content.

Ask the vet about appetite stimulant. It won't cure your kitty, but it might make her eat without the force feeding.

Good luck to you and Ditte.