Sarah Manley is a member of Wikia Staff (both in the real world and my fiction).
Lots of Wikia Staff are mentioned in The Fall, but none are named. The only reference to Sarah Manley is that she signed one section of the Wikia Log - presumably she wrote it. It is possible she was one of the staff mentioned.
Her fate is unknown, but it is likely she died when Wikia was burnt down by Lewis Dodgson.