For one, most of the spiritual entities seem to be tied to the ether, fire elementals included- now, that doesn't necessarily mean that earth elementals must be tied to the ether, but it seems very likely to me that they are.
For another, presumably there is more than one earth elemental. It's not a unique type of being. If there were others, Jones (in her vast, vast time alive) would have met at least one, surely. And if she hasn't had a chance because they only recently came into being with humans... then that means she isn't really an elemental, is she?
The possibility is still there, but I find the probability to be exceptionally low.
My guess is that Jones is basically something entirely different in the Gunnerkrigg cosmology. She is not human, she is not an ether related spirit. The existence of Jones hints at something else that we haven't been introduced to yet.
I almost wonder if this is somehow related to what is up with Kat. Kat seems entirely unrelated to the ether as well, and yet there is obviously something very strange about her, from the regard of the robots to how Zimmy sees her.
Here's one silly possibility I want to bring up: Jones said she doesn't know what she is. So how does she know she isn't a robot?