I've also never seen or heard about a room by that name. Having just gone back over my floor plans again, I came up with one possibility: the large room located between the Queen's Audience Chamber and the Royal Closet just off the Minister's Staircase. In old floor plans from prior reigns this room was labeled a sitting room for a senior lady of the court (Miss somebody or another - I can't recall).
The traditional sequence of rooms in a royal palace's state apartments was: Guard Room, Presence Chamber, Audience Chamber, and finally one or more withdrawing rooms or cabinets. So it would make sense to me that the room preceding the Queen's Audience Room would be the Presence Room.
Thoughts?