I believe this book was from the 80s after the real case of day care abuse and Satanic worship came out. This was a girl (early teens) who has a little sister or brother enrolled in the same day care that she attended. Things her younger sibling says to her begins to trigger memories of her own time there and the abuse (I believe sexual) that she suffered. No one will believe her because the teachers are so well loved. She has to find proof of the abuse by speaking to the children who attend the school.
Stump the Bookseller
New format, same book stumper solving.
More of a “maybe this will help” than a real clue, but I vaguely remember reading a book like this. I thought the author’s last name was Ferguson, and it was in the teen section. If it’s any help, her other book was about a girl whose preschool sister was thought to have died and was buried. But the family was Jewish, so it was done before sundown. The older sister was suspicious for some reason (and a suspect in her death) and she managed to discover that her sister had been given something to make it look like she was dead and then somehow taken out of the coffin before she was buried and adopted out to someone on the black market for a large amount of money. It might even be the same story, because I also remember allegations of abuse.
Anyway, good luck!