Haven't read the entire thread but did read the suggested updates, so hopefully won't repeat.
Did anyone notice the hotel video on the first page? The shower wasn't in the room. It seemed to be in a different location.
Something I think that's important is that in the elevator she had no purse, no keys, and slip on shoes like you might use in a shared shower? With a shirt tail hanging out like you'd hurry to leave a shower. But, her hair didn't seem wet so unless she'd been moving around a while, or hadn't yet gotten into the shower, that wouldn't apply.
But, a woman alone would keep her keys and purse (or whatever she used to carry money and id) with her. The only explanation I can find for being without them is either someone else watching them for her, escaping in a hurry, or being stoned out of your mind. Wonder if they were found and if they were, where? That is a biggy.
When she gets on the elevator, there doesn't seem to be the desperation that's shown after a couple seconds when she starts pushing all the buttons. When the bottom green one lit up, she relaxed, then tensed and peeked out the door. Almost like she feared someone was outside holding the button, keeping it from moving, or that she heard something....or that she was on a drug like ectasy, or pcp.
If she wasn't on drugs, I'd guess the frantic pushing was an effort to get the elevator to move with it stopping at each floor, leaving a stalker to wonder which floor she got off.
There just wasn't the sense of urgency you'd expect when she first got on, if she was being stalked.
Either way, they can find out if she was dead before she was in the tank, or if she drowned inside. It would take longer, but they can find out.
Feel free to delete. Just wanted to toss out a couple things I didn't see mentioned.