ZUN has stated in a Livestream that the fairies in Sikieiki's stage, including Lily White, are all simply cosplaying as the judge, and specifically states that there was never an individual Lily Black to start with.
"Lily Black" and Lily White both appear as mid-bosses in Fairy Wars. However, this does not contradict the above as the two are never seen together at the same time. By comparison, Daiyousei and Lily White are seen together at the same time for the mid-boss battle of the Extra stage.
There are 63 people in the United States of America named Lily White.