Emma got a breather between two groups of people coming to congratulate her on the grand opening and she decided to use this time to ask Tiffany if everyone arrived.
"I'm going to check on Tiff…", Emma told Charlie before walking down the hallway which is closed away for this event. That is the hallway where offices are, and they didn't plan to allow outsiders in that area because there are computers which are already connected to the LA Medical Center network and they can be used to access sensitive data of the patients. Of course, everything is password protected, but you can't be too careful.
Charlie didn't go with Emma, because they have security personnel at the entrance to that hallway and technically, no one without authorization can access it.
One of the offices was used as an 'event-planning-central' and Emma is confident that Tiffany is there.
Emma entered the office and froze.