It's unclear how much Rose will actually change, other than her looks obviously. Because her current plan is to infiltrate the cheerleaders to prove there's mind control going on. OTOH at the same time she's getting addicted to Richard's D, so
There's going to be some kind of 3rd chamber, but we don't know how many and what kinds of rooms there will be, or how many mental changes there will be.
Just based on what I think will happen, the 3rd chamber is going to be the shortest. But maybe I'm wrong.