The Angel of San Bernardino - S3-E20
Other mistake: Lucifer's obsession with Bones is highlighted here when he confronts someone as a killer only to realise it's because he's an actor who played a killer in the Bones episode Intern in the Incinerator (a role Scott Rinker did play in real life). Kevin Alejandro (Dan) and Aimee Garcia (Ella) also played roles in Bones, which Lucifer never comments on. In fact so did Jeremiah Birkett (Lee Garner, "Mr. Said Out Bitch").
Chosen answer: She has been keeping that whiteboard for probably the duration of the series. She has been piecing together clues the whole time. It was more obvious with "God" when she was fishing for info and mentioned the best hugs ever. I feel it was intentional to just spring the whole "I knew it!" in the last episode (s). I personally was hoping she would get a better sense of "closure" as she was really the only main character not in on the deal.
kayelbe