That fellow congregant, aware that the church had done nothing and that local law enforcement had done nothing, and that the family was going on Oprah to promote themselves, sent a copy of that note to the show's producers.
The producers killed the interview and reported what they found to law enforcement.
Basically, the woman from the congregation found a way to go over the heads of the local Duggar enablers and seek justice.
We don't know what the note says or what the circumstances of the book borrowing were, but it may have been a "message in a bottle" from a victim to an old lady whom she thought could help her.
Source? I heard that it was notes in a book the father had left by mistake. The “congregant” went and snitched to Oprah hoping to embarrass the family is my guess, instead of sending the note to the local police who would have handled it. So I really suspect the congregant of their own agenda. Why is the story out now by the way? Hmmmmm?