Search of the Forgotten
Lilith was the first to follow Lucifer after the fall. She couldn’t reconcile the reason for casting Lucifer so far down when he had suggested the better plan, in her opinion. So she became the right hand (though she still thinks it should be the left hand, every time she gets a chance to remind him) of Lucifer’s reign in Hell. They work well together, Lilith taking care of the dirtier side of getting souls to Hell. Because that’s what she likes. When she’s ready to kill, she adopts a different personality, Abaddon, who can take care of business and still maintain a smooth outward appearance. So she keeps watch with Lucifer, even when it’s vacation time.