I like your theories on Cass, but how do we know that was even really her that came out of the doorway when the house of yesterday's tomorrow was destroyed?
Because where would the fun be in that?
And how would that impact Cassandra’s story? “Oh she was tricked off-screen and locked away while someone else took her place, what a revelation!” Nah. It’s far better to try to figure out why a character did something and how this is going to affect them.
There’s obviously something off about her but that’s because she had a whole episode of development without us seeing any of it…an episode we will undoubtedly see at the start of Season 3. :)