Fascinating case -- right up my alley!
I’ve been retired for some time now. However, I used to work in a dual diagnosis department where I specialized in addictive and psychiatric disorders. The elevator video shows Elisa to be having a psychotic episode in a manic (positive symptom) phase. Her grossly exaggerated and repetitive mannerisms, along with her apparently talking to invisible beings (likely suffering from visual and perhaps auditory hallucinations) indicate that. Note that psychosis can be emanating from Elisa’s own psychopathology and/or induced by drugs (e.g., Ecstasy, LSD).
The distinction between bipolar disorder and schizophrenia is a hazy one even within the psychiatric community. (See explanation of why there is ambiguity at
http://www.dnalc.org/view/1252-Differences-Between-Schizophrenia-and-Bipolar-Disorder-1-.html). Hence the confusion for laypeople to judge whether Elisa suffered one or the other, or whether it was comorbid, is understandable. However, given that Elisa appeared to be largely functional and able to carry on ADL (activities of daily life) on her own, it is likely her doctors diagnosed her with bipolar disorder, rather than schizophrenia.
You can read more about the specific symptoms & criteria for these disorders in the industry standard diagnostic & statistical manuals for psychiatry (DSM IV-TR and/or the new DSM V which is due to be out in May 2013; both can be ordered in Amazon.com).
Re: sleepwalking. In my opinion, based solely on the elevator video, it is highly unlikely she is suffering from sleepwalking as sleepwalking generally entails subject doing routine activities such as cooking, eating breakfast or driving a car. Elisa was clearly seen on elevator video to be talking animatedly to something invisible. There was no person/shadow in or outside the elevator apart from Elisa's own. Also it is notable that Elisa leans downward as if she’s speaking to children. Coincidentally, I had in my past work observed many schizophrenics and schizoaffective patients describe seeing “little people” (adults of short stature who are invisible to the non-mentally ill) running about, following and interacting with them. Such imaginings are indicative of visual hallucinations.
Of course her mental condition helps us understand Elisa’s state of mind in the hours prior to her death, but it need not be the proximate cause of her death. Could be that because her mental state was compromised, someone else took advantage of her.
My primary theory of her cause of death is that Elisa suffered from severe psychosis and she threw her clothes and sandals into the water tank and then dove in for a swim. Her death was unintentional, an accidental death by misadventure.