Maybe she wants to be fed and empowered like the lich king because she thinks she's the only chance Azeroth has got against whatever evil has Azeroth bleeding? I imagine in her mind it's going to take a lot of souls to pull out the sword in silithus. She'll happily sacrifice herself to that task taking on power that'll probably obliterate what's left of her own free will and fading sanity while of the belief that she's helping...
She could be joining team with Azshara and Nzoth for who knows what. Probably some void lord somewhere saying hello and trying to enter our realm through the tear in the side of Azeroth. If not corrupting the planet itself to become a lord or a gateway stabilized and manifesting here through the sickness and escalating chaos.