Lucinda thought that Lucifer's death would bring peace to everyone, including herself. She thought that the reason she had romantic feelings for Lucifer, her biological father who happened to be her husband, was because he had been messing with her mind. After his death, she realized what kind of a mistake she'd made. Not only did Lucy bring about the end of the worlds by breaking the seals and summoning the horsemen, but she also lost a part of herself with a man she shouldn't have but loved.
What if death is just a part of the big plan, God's plan? Or what if Lucifer's death wasn't a part of that big plan at all? Until she finds God—if he wants to be found—she will not know the answer to these and many other questions.