@baasinsimple gave some interesting insights and distinctions about anti-heroes and anti-villains
But i think she may fit better the wild card trope. She may be in the conflict for her own personal goals, and don`t care about the conflict per se. Maybe she is in for the money and changes sides depending of who pays more. Or perhaps she cares about people from both sides. Maybe the villain may be her lover and the hero her sibling. Another posibility is that she loves the thrill of it and cant stop doing it, so she will choose the side that is more entertaining or facing a more interesting challenge.
She may even lean towards the neutral alignment. Caring only about herself and the people she loves.
