Wait, its supposed to be adria?
I remember her looking... different.
As for who's side she's on, diablo's. She's an utterly obssessively loyal servant of his, the entire plot was to fuck over all the other demons in order to give diablo control over them in one body.
A better example IMO would be Zoltan kulle Dude was 100% right about EVERYTHING and had humanity's self interest at heart.