Okay, the game makes it pretty clear that the difference between a sorceress and a regular woman is that a sorceress need not junction a GF nor draw magic to use magic. This point is emphasized when Rinoa develops the Angel Wing limit break after becoming a sorceress. So why the hell can Selphie use random, undrawn magic even without a GF equipped with her limit break, Slots? Is there something she's been hiding from the party? Perhaps, Selphie=Ultimecia?