Can we all agree that the floor she is most likely to be on is this one?
Same wooden horizontal bar, same wall color, same floor, same vertical columns, same light fixture seen in the top right corner in the elevator video.
And the mirror? Elisa is definitely looking into it directly numerous times in the video to see further than she can from where she stands.
So now, can anyone confirm WHICH floor that picture is from?
Second, I think we can agree that Diaz is on the 14th floor (you can't trust a single report, same with the naked body aspect), and that therefore means the sound her heard was above, and the drain blocked and flooding between the 14th and 15th floor.
This makes everything far more logical to me.
If this is all true, then I believe the body language makes even more sense, and once again leads me to believe that all talks of drugs and psychosis are way off:
1- Elisa was invited to fool around on the rooftop by someone, probably a youth she has been talking to earlier.
2- She agreed, hence why she ends up on the 15th floor. She may or may have not actually gone on the roof when the video has started, and if she did she may or may not have made the white graffiti that has similarities to her handwriting.
3- She decides to go back to her floor. She may or may not expect the person to follow her. If she was on the roof before, it is possible that she took a head start when deciding to leave, and hence might be waiting or not caring if the other follows, she has decided she is not staying there (thinking they might get caught by hotel staff).
4- When the video starts, she is not in a fearful mood, she is in fact even slightly cheerful (as seen by the way she makes an exaggerated motion when pushing the first button, floor 14th). She was having fun or a laugh with the person(s), but is merely done for the night, heading back to her floor.
5- The reason she hits multiple floors is because Elisa read up on tips about staying safe since she is a woman traveling solo:
Travel Crime Prevention Tips
It's just a safety precaution, she is either expecting the person she was with to follow or not to follow.
6- The doors don't close, because she hit the door hold button. She thinks the person is the one who kept it open. But after waiting a short moment, the person doesn't show up.
7- She thinks the person is fooling with her (normal to expect this, the person is certainly more of a prankster than she could be). This fits with the playful prior attitude. The way she looks out quickly indicates play, not someone truly afraid. But not seeing anyone, she's a bit worried, because the doors could not have remained opened on their own in her mind, she thinks the person moved back hiding behind the corner, which is creepy to her.
8- She hides a bit and waits.
9- Decides to peek out, and as she peeks out the person shows up.
10- The person walks towards her, and she steps backward instinctively to prevent the door from shutting and to make room for the person to come in too.
11- Then she steps forward as the person stops as well, realizing the person is not going in, so she isn't going to stand inside the elevator, as the person is probably talking to her.
12- The person is trying to convince her of something, her hands let go, and all she is thinking is "ugh, I really don't feel like it", putting her hands on her head, trying to indicate she isn't really in the mood, a bit fed up.
13- When she goes back in, her hands on the wall, smile on her face, she is thinking trying to show that she is tired (more emphasis than hands on head), and not angry, but tired and not interested.
14- She pushes numerous buttons again. Nothing works.
15- She steps out again, resuming talk with the person. Explains the elevator doesn't work, laughs at 2:10, then cracks her fingers to undo stress or she is listing something (have to get up tomorrow early, etc.).
16- Puts back her hands on her head as she leaves with the person, giving up.
A loud noise is also heard at some point: possibly someone stepping or jumping down onto the tank from the top of the maintenance building, rather than climbing up the ladder? It's possible the person climbed up the maintenance building ladder before even seeing the water tanks, and then jumped on the tanks himself from the top of that building, causing a loud bang. After being on it, he realized there is a ladder and asks her to go around and up the ladder if she doesn't want to jump.
Not sure how Elisa ends up in the tank though.
It's also possible that the person killed her on the top of the maintenance building, and dropped her body on the water tank (which just happens to be one of the two that is the closest to the maintenance building), causing a loud reverberation. Then puts her body and potentially some or all of clothes in as well.
I am certain she was dead when inside, otherwise she could have banged on the tank and screamed a lot, which would have probably reverberated loudly.
Then her clothes possibly go through the drain inside the water tank, causing a flood between floor 14th and 15th.