Well, at the start, when they are finding out about Dora, Rust says "She sounds like she was tired, someone who was torn up and walking on her last legs. She was just an easy target for him." Then rust pulls that other file with a lady that had that spiral on her back, and it was the same story, someone who was just beaten down and looked at life as something that was pointless.
That's actually part of the reason I started thinking Dora was kind of bait for Rust specifically; because of all the shit Rust went through, he's that same type of "none of this matters" personality, so this cult's nihilist philosophy would appeal to him. So they put her out there like chum in the water and then left him the little nets to keep him running around, wanting him to eventually go mad so they could convince him he needs to "break the cycle" (IE they want to ritually kill him once he fully loses it.)
Then again, the thought of a conspiracy, even a well organized one, slowly wearing someone down over 17 years? Soundsreallyfar fetched. That's a long time to play a game with someone. So maybe Dora and the ones since were just there to show their followers the "law" wasn't a threat to them.