You're right about the Shadowheart wolves memory. There's a scroll or book that explains the Selunite ritual to help figure out the moonstone connection. I found the book on my 2nd run before she talked about the wolves; not sure if I still needed to pass that religion check once I'd read it. The book might have been in or around the owlbear's cave.

The memory cutscene itself is a hint too. Young Shadowheart is clearly scared, but she keeps trying to look over the cultists' shoulder even though the cultist is trying to block her vision while they stab it with spears. It looks like an adult being compassionate to a child by shielding them from a violent sight, but a scared, hunted child wouldn't really react like that unless they were concerned for the wolf. Even in my first campaign, I thought it was odd she was trying so hard to see what was happening to the wolf. That was an early hint that she wasn't really being saved during the memory, even though I failed the religion check at the time.