There's nothing in the game that gives a name for the GF she found--in fact, Selphie specifically says that she doesn't remember its name. Personally, I suspect that it's an ice-aligned GF, given that she found it in Trabia (and there's a lot of snow there), but that's as much a guess as anything else.

Selphie has a high compatibility with the Tonberry King, if I recall, but you'd have to explain why it was in an area (Trabia) with no Tonberries, and how it got there. Actually, it almost sounds the beginning of a funny story...but I suspect that had it been Tonberry, Selphie would have had something to say about it.