#milliemayfair

While the fandom wiki lists her as alive, she is unequivocally a ghost throughout the season. Let’s break this down.

First off, in every scene she is in, she is wearing the exact same outfit. Even when Carlotta has gotten ready for bed or just woken up in the morning, Millie is still fully dressed in that same outfit. Days later, same outfit.

She is never seen around anyone else in the family besides Carlotta and Rowan. She doesn’t go outside or participate in any family events such as the funeral.

Rowan only first encounters Millie after being guided by a butterfly/moth, a psychopomp which is a guide between the living and the dead. This is also when Rowan first feels the magic of the house and is lead to Lasher’s key.

In The Thrall when Millie is in the bathtub, she says she can’t hold on without her sister Carlotta and as she is fading in and out of reality she says it feels like she is “dying all over again”. This suggests she has died before.

After The Thrall when Carlotta is dead, we never see Millie again. If Carlotta was all that was tying Millie to the material world, her death would understandably cause Millie to disappear.

But the big clincher is before all of that, when Rowan discovers her own name on the family crypt. Just bellow her name, is Millie Mayfair. Since the names seem to be listed in order, this suggests she is alive in Deirdre’s flashbacks, but then passed away sometime after Rowan was given away and supposedly died.