Will this be a spoiler? BFF reading for the first time, want to tell them a theory about Kaltain

Hello, my roommate and best friend is reading Throne of Glass for the first time and she just finished Throne of Glass and is about to start Crown of Midnight. She has read all of ACOTAR, and I want to tell her the theory that Kaltain could be the suriel, but I do not want to spoil it for her. I was going to wait until after she gets the cloak from Celeana in the dungeon (I know i would kind of be spoiling that she dies, but I could play off that she lives out her normal human life somehow), but if that would still leave spoilers I would rather wait until Kaltain actually sacrifices herself. Can anyone give me some advice? Thank you!!