Unless Airdorf stated explicitly of such, why is it assumed that the Elevator Lady is definitely not related to Gary's satanic cult activity? That she just happens to be there. Just because she doesn't appear as an apparition he summons doesn't necessarily mean he didn't appoint her into the world. Similar to the elevator demon, she easily could have emerged from the openings Gary created and he decided to let them dwell and roam the apartment complex. It could very well be that they are demons summoned by Gary, but perhaps secondarily or unexpectedly. So they just do their own thing.