I've had this issue as well, and wanted to say there is another situation she can spoil it. When you reach Pearlwood Bluff and find evidence of Naasitaq, she also brings up Thaos by name, despite the fact that you can (as I did) reach that point without even entering the catacombs.
I also had this, once I left the sanitorium I had a vision where he was called by name, despite the fact that I should not have known it.