The Warrior of Light is not tempered by Hydaelyn.

[Lauront]

She needn't even be "evil" - I don't really consider Zodiark or the Ascians to be such; it's more that their goals (particularly the latter's since we've never heard from Zodiark) and ours conflict. By the looks of it, they consider the existence of anything that came to be after Hydaelyn banished Zodiark to be illegitimate, and she is no different to any other latecomer Primal to them. Assuming that there isn't anything more to their motives, that is.

However, she may be possessed of the same sense of conviction many Primals have about them, and if it is the case that the Rejoining must go ahead (even if not by the Ascian methods) in order to stabilise the world and prevent further floods, her hatred of Zodiark (and inability to grasp that they're both Primals) may cause her to get in the way. Both are Primals so both should be, in essence, entities which can be summoned again, provided that doing so would not destabilise the planet itself.

Quite frankly, I'd be happy if they go down this route and I don't particularly care if she ends up not being "good", as long as they make it interesting. I don't need cartoonishly good or bad characters for the story to be of interest.