That was answered.
Men see what they want to see, women see things as they are.
She addressed that in one of the episodes.
I don't know that I accept that as a full explanation.
Like I said, she obviously really looked like that in life. Both evidenced by her file when the detectives confront Constance, and the fact that her husband lusted after her the way he did
while she was alive. When they show Constance shooting them both, she saw Moira as the young vixen.
No one else in the house ages a day beyond when they died. Tate hasn't aged a day. The Montgomery haven't aged a day. Why Moira?
She only became the old hag as a ghost. Why?
If anything, "Men see what they want to see, women see things as they are" just confuses the issue more, because Sani's dead on. It's completely the other way around. The men see her as she was in life, and only the women see her as the old glass-eyed woman.