Yeah, I can agree with that. How I think it should be gone about, is that Shadowheart will not outright confess unless you confront her with sufficient evidence to question her motives and do it in a way which does not make her feel like she is under attack. Say during each encounter where she interjects, the player potentially has the opportunity to become suspicious of something, given they make the right dialogue checks. Then after enough checks have been made, they are able to confront her and bring up all of the irregularities they have noticed and ask her to explain them. It is obviously not an easy scene to write, but it would (in my opinion) make for a much more natural way of uncovering who she is. The uncover should also either come after chapter 1, or very late into chapter 1 and if the player never does uncover it, there should be some consequences much later in the game.
That could work really well, rewards players for actually interacting with their companions and gives it enough time that it actually feels like it makes sense that she could trust you or come completely clean. Cause right now it is essentially pet a dog a few times and she will spill her guts. I think somewhere around the Tiefling/Goblin Party, or after it is the best time to get that first reveal or confrontation out of the way because it seems like Shadowheart's whole part to play in BG3 is having secrets and mysteries be revealed one by one, as there is a list past her worship on things that players don't have the answers for (but can easily speculate on).
Also edit: I just realized the Mask thing might not be such a bad suggestion because he is dead, and an adherent of him has gained his divinity and position. Meaning it could be plausible for someone to worship a dead god and still get powers from Drasek Riven, but it would instantly set off red flags for anyone who knows Faerun God Lore and/or anyone who passes a religion check to realize its a dead god. Would create a piece of evidence against her while not being the worst lie, especially since in other editions people were able to get divine power from Io who was dead at the time.
