Book that's like To Kill A Mockingbird but isn't that

A customer came into our library today asking for help. She remembers reading "To Kill a Mockingbird" with her granddaughter almost thirty years ago, and has a distinct memory of a certain scene:

The kids had gone to a religious revival the day before, and were playing in the yard the next day based on what they'd seen at the revival. Dill was preaching and baptizing just like the preacher at the revival, when they were interrupted by Atticus coming home from lunch - and bringing along the preacher from the revival, who saw them pretending to be him! They laughed and laughed, it was so funny.

As far as she or we were able to determine, this never happened in To Kill a Mockingbird (or To Set A Watchman.) But I was hoping if it was another book she'd gotten mixed up with that one, we could maybe track down what it was.

Never mind! Looks like it's in Go Set A Watchman after all, the copy I was searching in was just incomplete.