My friend, I’m afraid you have me quite mistaken for someone else.
While it is true some scholars believe that the Night Mother, bride of Sithis, is Mephala, it simply makes so sense. Within the last 200 years, this Night Mother, was alive and supposedly copulated with Sithis. There is no way a Dunmer woman is Mephala. Mephala is a god, alive since the beginnings of time! She would have no need to marry some master of the void and sacrifice any of her mortal children to him. It just doesn’t follow reason. Nor does the supposition that the night mother is somehow the leader of the Morag Tong, or in any way associated to Mephala. In fact, none of these bizarre links really work if you look at them objectively.
While I appreciate that the followers of Sithis are a pleasant group of people looking to strike down the lives of the unsuspecting for money, I am hardly the type of person to join a cult that tries to destroy the world. I enjoy the world and the pleasures it has to offer me.
I do wish you luck finding this other person.