Otherwise the fact "Rigma" is two syllables and only five letters, is a good thing to me. Ironically, I just contradicted my outlook with my suggestion hehe.
I think we could find something equal or better sounding and meaningful than Rigma, but Random House made a good choice. If we can't find another name, keep Rigma.
I do agree with AmericanPianist though, Gildar flows better thna Rigma. I'd rather not associate anything from Final Fantasy with Elemental just for bounadries sake mentioning it, but its a great name. Rigma though feels like it is far more relevant to the title Elemental than Gildar. Gildar sounds more medieval and renassiance-esque to me.