I'm going to go with theory that she stripped naked, hid her clothes in the garbage, and ran up onto the roof undetected, and decided to masturbate in a tank of water while drowning....because, you know, she's mentally ill. In that moment, she decided to drop her plans to go to Santa Cruz, forget about the gifts she bought her family, and just kill herself in a tank of water, because that has always been a dream of hers during periods of psychosis. She wrote the graffiti prior to entering the tank, because she was referring to herself.
Either that, or she met up with a long lost twin and killed her in the water tank, and she's now on some tropical island living her life in tranquility. We must consider all possibilities right?
Seriously though, it's futile to treat her death as a result of her mental condition, because you can argue whichever way you want, and come up with an infinite number of possibilities. We need to analyze her actions in terms of motives and her past history, as if she was a rational human being.