Some of the elements of this picture- the talon-like fingers, the large spiky shoulder pads, the expression that looks like she's glaring at the viewer- almost make her look like a villain.
She does have an evil queen vibe to her. Aside from absurd magic stats, her special move was "banish", a skill that could force most random encounters to flee. As BoFII was a game that employed triage in it's game and dungeon design, avoiding unnecessary/unrewarding fights was pretty handy. Otherwise you'd get worn down before fighting a rather unfair boss.
I think it's supposed to be more of a contrasting element thing, like a half-fallen angel. Nina goes from just having wings to having four sets of more clearly angelic wings in a more twilight-red color than her normal "black" wings and a much more elegant dress and animations that seem more regal.
Nina in BoF2 was a symbolic "corruption" of the previously "pure" bird tribe caused by the previous Nina apparently marrying the previous Ryuu and intertwining the bird and dragon tribes. BoF2 Nina is no longer the "white mage", but the "black mage" of the party. She has to fusion dance with the wind and holy shamans to get this form, which means it's symbolically meant to be her getting more "holy", not less.
