Alice Isn't Actually Brainwashed
This one is a relief. Alice Cooper isn't brainwashed by the farm after all. She's working with the FBI to bust the cult's leader, Edgar Evernever, for harvesting the organs of people who join the farm. This whole time, she's been earning Edgar's trust in order gain intel. (I can't believe she'd go so far as to throw her own grandchildren in a fire to prove her feigned loyalty, but whatever — it's Riverdale.)
And the FBI agent she's working with is none other than her long-lost son, Charles. That brings us to the next major shocker on the season finale . . .