I was just coming on here to post the same thing...is it possible she is maced or stun gunned / tasered!?
In regards to this. I had just shown my colleagues this comment, and asked their opinion on the matter (serving military, etc) and they state that it is an absolute certainty that she was not affected by either.
Tasers, whether hand deployed or shot, will drop most people due to their effects on motor nerves (simplified). While I agree the quality would not allow us to see taser prongs if deployed via launch, we may see the wiring running around the corner of the elevator door (may be far reaching here).
As for mace deployment, she shows no normal signs that she has been affected by it. At no point does she react in a state that the majority of normal, unwitting citizens do when confronted with compliance oriented devices.
As noted in previous posts, I am currently in a sector that focuses on threat risk scenarios and so forth. Analyzing this video (however poor the quality is), there is no indication she acts in a panicked mode. In my assessments of risk, threats and reactions, people rarely flee into confined areas. Elisa at no point seems to flee in this video, however if we were to assume she was, the likelihood of her entering this elevator is very small indeed.
Her continuum of body language indicates no definitive source of a third party. At certain parts she will react left, and then right. At 2:28 we see her finally exit left, whereby stepping on the blade of her left foot and sweeping her right foot over. Note this is also where people are believing another person appears, but if you watch and assess it as per the above, it is actually her foot on the blade, which is what kicks up the sandal.
Lastly in reply to the person who stated that physical injury would be present for murder identification, it is completely feasible that submersion in water, and advanced decomposition would degrade physical evidence on a body to the point of uncertainty (ie bite marks, strangulation, etc).
I wrote this on an iPad so I might have a ton of spelling mistakes and make no sense.