My friend just had a paranormal experience. What is it?
Sorry, that tale does not pass the paranormal experience threshold. Elevators or lifts as they're called in the UK, many times come in banks (2 or more). My guess she was looking at her smartphone, or mobile in the UK, and just lost track.
She is mistaken. People make mistakes, but they just don't disappear into nothing.
It could be a vision warning of something which will happen in the future, like one day those people will be in the lift and there will be a gas leak in the building and it will all be engulfed in a massive fireball and they will be screaming horribly and die.
She was either mistaken in thinking she saw several people or she likes to make stuff up for a laugh..
Ask her to describe how many people and what they were wearing. Clothing is a big help in determining if it was a ghost event or something else. Ask if she recognised any of them as being current employees. If not then it is more likely. Research for accidents at the property address in around the dates of the clothing styles. It's a good starting point. Also check for any fires at the building - they could have been trapped in there. Hopefully you will find some recorded reason for this, otherwise it could just be an active imagination. Possibly all those people did die in the evevator.
There are a plethora of things that could have happened. 1.) She might need her head checked. 2.) She may need more sleep. 3.) Aliens abducted her (which they do suddenly and mysteriously) 4.) The elevator was filled with holograms, either by ghosts/demons or aliens projecting people. 5.) A glitch in the system (of the 3rd dimension or Earth) 6.) Parallel universe crossing over briefly (like the Mandela Effect) The are signs when determining if it was aliens or ghosts and other entities. Like for example, if repeatedly she sees the same numbers on the clock (like always seeing 11:11 or 12:34 or 4:46 everyday when she looks at the clock), that's an indicator of aliens. Ascending numbers 12:34 are always a better sign than descending 5:31.
Either she imagined it, was mistaken, or it was a paranormal experience. There are strange things that happen in life to some people, and there is never going to be an explanation.
Christian in Jesus
Sure, it is a game that super naturals play. There is a missing persons case from Southern California, Ms. Elisa Lam, I think that is what her name is. It will explain why you witnessed the phenomenon. She was meeting with some friends that claimed that they had intel on time travel. What it is really is taking a walk into the alternate dimensions that the dead walk in. That is why some psychics can see through the "veil" and capture images from realities that don't exist. This is how satan deceives making you believe that we are in a locked tight dimension. Sin and hate bust holes in our dimension. That is what CERN is working on. They collide particles to produce chaos in order to bust holes through our dimension. So your friend from a distance was looking into a busted hole. When she approached and came closer then reality prevailed. That is why she saw nothing. It is known as "being taken out of reality".
There is more chance by far that she made a mistake. She saw them in a quick glimpse but she boarded the elevator next to the one the people got on. If she worked there for years, she possibly knew the people and knew they were at work the next day. By the way, in the UK, we call them elevators "or" lifts. NG only found out we spell sceptic differently a couple of days ago.