3. In contemporary practice, this room would be called the Telestial
Room (or World Room), not the Terrestrial Room. It's possible that Emeline has
misnamed this the Terrestrial Room because it represents the earthly--hence
"terrestrial"--realm. (I know of at least one other temple exposé
whose author appears to have been confused by the peculiar Mormon usage of the
word "terrestrial.") By this theory, the room Emeline calls the Celestial
Room, where she saw Brigham Young and other members of the Twelve, would actually
be the Terrestial Room; and the room after that, where she says "not much
of interest transpired," would be the Celestial Room.
On the other hand, it would make sense for Brigham Young to have appeared, playing the part of God, in the Celestial Room, just as Emeline describes it here--though in that case, I have no idea what the room after the Celestial Room would be. (An exit chamber, perhaps?) It's possible, of course, that Emeline's memory is confused, or she may have received the endowment during a period when the ritual drama was still in the process of development.