Phantom's Tutorial

Or the dark haired one's trying to prove that the current Empress isn't the actual empress.

Yeah but Nexon being Nexon would never ever get rid of our current empress. On top of that, Hilla's a Black Mage general, and her guards are dressed in Black Mage colours, and have no faces, implying that they're possessed. It's obvious she's the evil one.
That and the Skyia was given to Phantom after Aria died, and I doubt he'd be willing to give it up easily.

It's more than likely that Hilla's playing a trick here, trying to get the people of Ereve to believe she's the actual empress so she can bring about the "dream future" from the Temple of Time.