Why won' otherwise healthy 13 y/o pomeranian eat?

There can be a multitude of things that are affecting your dogs appetite such as an illness or it could simply be picky. Could you give us a little more information so we may be able to get a better understanding of what's going on?

Had to spread the rep but I agree with Silver.

We cannot give an answer based on the info you've given.

Have you taken your dog to a vet? How long has this been going on? Have you recently changed dog food? Has your dog undergone surgery, been on meds, hurt herself any other way? Is there a new member in the family? Have you recently moved?

We really need a lot more info.

Older Pomeranians are notorious for losing their teeth. Take your Pom to the Vet and have him check his/her teeth as well as the normal Vet check up.