Pestilence is one of the horsemen of the apocalypse, she is a germophobe contrasting against her attribute which is sickness and disease
Pestilence first appears in "The Coast". Natalie bumps into her, to which Natalie apologizes. Pestilence then tells her it's no problem and to have a good day. A few panels later Natalie is seen coughing.
Later on, because Natalie has gotten extremely sick Lucifer takes her to Vegas to speak with Pestilence. He attempts to gamble for Natalie's health but continuously loses. After Natalie dies of her disease he decides to make a trade with Pestilence. He gives her his wings in exchange for Natalie's body being purged of all illness.