This is my first post on this thread. I believe she died accidentally due to her mental health, possibly exacerbated by medication. I have seen people suggest both ambien and sleepwalking and agree that the video footage might be interpreted that way. Possibly she had taken ambien to sleep during a manic episode and experienced the crazy effects it can have. I think the hand gestures just before she appears to be counting might even be a swimming gesture, i.e. possibly she was hallucinating or dreaming (or, if medication was not a factor, just thinking) about swimming, which would link to the tank. Conversely, I also think it's possible she didn't actually understand, due to her mental state, that there was water in the tank. Possibly she got in the tank for some other reason logical to her not thinking she was lowering herself into water at all. The bit towards the start of the footage where she quickly puts her head out of the elevator and back in again - she was just trying to check if there was a reason the doors weren't closing without them closing on her. I have done that lots of times, sometimes they close quite aggressively so you avoid being in their path.