Why does Nicholas keep giving Angelique so many second chances? How many times has she promised to follow his orders, only to turn around and disobey him the moment his back is turned? It was a collossal mistake for Nicholas to bring Angelique back as a vampire - he should have left her "dead" after he removed her powers, let her age and die. It seems like he never learns his lesson.
Is it Nick's enormous ego that convinces him he can control her and that she poses no serious threat to him because he thinks of himself as being so vastly superior? Does he keep her around simply to continue feeding his ego with the power of that control? Or does Nick perhaps have few lustfull thoughts where Angelique is concerned? Does she have to be his slave in other ways??
In any case she is his downfall and if he were a tad more careful, or smarter, he would have dispensed with her. Why do you think he keeps her around?