Darn, I forgot about Riku giving it to her.. Well either way, I'm sure once you've actualy HELD a keyblade, That you get some sort of ability to wield it. It would make some sense seeing as how Terra let Riku hold his Key for a split second because he saw KHII Riku for some odd reason(And a strange man).
I know this is a random late reply to this topic, but idgaf.
If you gain the ability to wield a Keyblade just by being given it to hold, I'm expecting to see Jack Sparrow kicking some major ass in KH3, personally.