I've got an alternate solution in mind, myself, but it depends largely on whether or not Muse specifically wants to be a Pixie (small fey creature with at-will greater invisibility) or just some sort of tiny fey creature.  The Monster Manual III, after all, has the lovely CR 1 Petal (http://www.realmshelps.net/monsters/block/Petal) that's even smaller than a Pixie, but has better base stats for a Charisma-based spellcaster.<br/><br/>And since there are generally more templates that increase Charisma than there are templates that increase Intelligence, I should probably also note for Avorae's sake that the Lilitu in Fiendish Codex I has a special quality that changes its innate Cleric casting to be Cha-based, rather than Wis-based.  Something similar, but for psionics, could be created as a custom Archfiend special quality...