Annie is a minor character in Mary Kills People. She assists Mary Harris with her euthanasia service by scouting for people in need of her help, then vetting them before copying their medical records and passing their info off to Mary.
Very little is known about Annie.
She believes that people should have the right to choose to die, and that is why she assists Mary in finding people. She believes that Mary is doing a good thing, but that she just "makes copies".
She was Joel's first point of contact with Mary, and was the one to set them up together. It can be assumed she also assisted in matching many, if not all, of Mary's other patients with her as well.