Before we re-watch we have a mini-theory.
Mrs. D isn’t the real Mrs. D. We believe the Mrs. D that we are seeing is Sara Harvey’s mom, who is actually Jessica’s twin sister. She is after the girls because she know that Spencer killed her daughter Sara Harvey. I know this is a bit out there but this is the only thing that we can think of that would justify her being ‘A’ and trying to frame Spencer.
We’ll post more to this but first we must re-watch!!