Adele is very clever, and her flirtations with Alex is a wonderrful insurance against eviction.
If she is up against anyone except Alex, then the Alex supporters will be forced to tactically vote her co-nominee out. If Adele is attached to Alex, then she will not nominate him so the theory goes. Keeping her in will be a tactical advantage to Alex.
There is of course an Adele v Alex clash, but as Alex has survived two public votes, the housemates may consider nominating him a wasted vote.
Ergo Adele is virtually fireproof.
