She is Lila Rossi (or Cerise Bianca) being akumatized. You must know Volpina, Chameleon and Hoaxer. I've thought about an original akumatized form for her: Hell Queen, a demon-themed supervillainess.
And nope. She doesn't wear the Demon miraculous (non-canon).
This is the last draft for the upcoming Chloenette AU post.
Miraculous: Tales of Ladybug and Cat Noir belongs to Miraculous Corp.