Have we ever seen Deb's therapist in any different clothing, or interact with anyone other than Deb? (Also thought it was weird that she was in the background during the gas attack, but then again, the building was evacuated, and she does work in the same building)
I suspect that she's Deb's dark passenger.
Only problem though, that would mean that Deb has been going into an empty office all this time. Wouldn't it be locked?, wouldnt anyone notice?