In my opinion, there are only a few plausible explanations:
She flew down to LA with the intention of 1) meeting someone she met online, or 2) she met someone spontaneously while on her trip who lived in the Hotel Cecil, and that person introduced her to hallucinogens.
On what was likely the beginning of a bad trip (based on her body language in the elevator), she was either 1) taken advantage of and murdered by the aforementioned individual, or 2) she OD'ed, her acquaintance panicked, and subsequently disposed of her body in an effort to avoid responsibility for her death. The fact she was found naked in the tank suggests the former may be liklier, but its also plausible that she was having sex with the acquaintance in his condo, and he didn't bother to put her clothes back on when disposing of the body.
Either way, there's not a chance in hell she gained access to the roof and climbed in a freaking water tank with an opening slightly larger than a shoebox on her own in that mental state, and her acquaintance who did 1) murder her or 2) supplied the drugs which led to her death had an intimiate knowledge of the building. In all honestly, this suggests that the person was a hotel employee, or a resident in the building and friend of a hotel employee who provided the person with the key allowing roof access (I am a former DTLA resident, and I can attest that the view from the Cecil Hotel has to be awesome -- I'm sure some of the more brazen residents have discovered a way to get up there and enjoy it).
One more point: Main Street is *NOT* Skid Row. The heart of Skid Row is San Pedro and 8th, which is several blocks away. While transients do traverse up to Main Street, the bulk of them rarely pass Los Angeles Street, which is a block to the east. While walking on that part of Main Street can definitely be dicey at night, the Spring Street and Main Street corridors have changed considerably in just the last year for the better -- there are plenty of residential buildings, bars and restaurants on that street which are now inhabited and enjoyed by successful artisans, hipsters, etc.
In other words, I have trouble buying that a crazed bum followed her into the building. Her playful state in the elevator suggests that she was accompanied by someone who was also tripping balls.
