Here is a link to a Sim version of Selphie with details on her necklace, although it looks likes the creator's interpretation of it. I'm not sure there are any good screenshots of it in the game.

I don't think there's any canonical evidence as to what the GF Selphie junctioned with in Trabia, but there's no reason to assume there aren't more GFs than shown in the game.

Personally I would suggest Carbuncle, the two are both very bouncy and cute.

Good luck!