I believe it was suicide, although I do also agree that at most the police should have been more vigilant because of this and perhaps should be charged with neglect. Not only her own statement when she was being charged, but also the statement of others close to her (family and friends) have mentioned that she suffered from depression and had been suicidal in the past.
For the amateur scientists here that question how she could be hanged by a garbage bag ("Jailhouse garbage bags at that." -honeyflower93), if you feel that she would have ripped through the bag if she attempted to hang herself, you should see no trouble for a person to rip a phonebook in half. After all, even a child can rip a piece of paper in half, right? Except that what this logic fails to realize is that the formation of the bag provides different properties, just like a single piece of paper has different properties than a book of paper. As these amateur scientists have pointed out, it is pretty easy to rip
a single layer of a plastic garbage bag. However if the bag was bunched together like twisting it into a rope (which one would think you'd need to do in order to attempt hanging by it), the bag becomes much more difficult to tear. An easy experiment to test this would be to take a garbage bag, twist it into a rope, and then see how easy it is to rip the bag in half; I'm guessing that it is just as difficult as trying to rip a phonebook in half too. So I don't question whether this could happen in a physical sense, but I do question why items that potentially lead to a suicide would be within her jail cell esp. when considering that she was known to be suicidal.
As for whether her initial arrest was correct, I actually have mixed views. On face value of the reports, it sounds like she may have made an illegal lane-change (nothing serious, at least nothing worth worth jail-time). The officer, during the pull-over, the cop was initially just going to give her a warning but first asks her to put out a cigarette that she is smoking in her own car. When she refuses (nothing illegal there), he tells her that it is now a lawful order for her to step out of the car and things escalate from there, finally ending with the cop charging her with resisting arrest. Again on the face of this, it seems like the cop escalated it pretty quickly esp. for such a petty offense like an illegal lane-change. However when the toxicology report was released showing elevated levels of THC (the psychoactive molecule in marijuana), then I started to understand some of the questionable facts in the arrest. For example, people that smoke marijuana may smoke cigarettes in order to disguise / mask the odor of marijuana; for this reason I can understand why the cop may have requested her to extinguish her cigarette. Also a couple of times (before the escalation) the cop asks her if she is all right, perhaps because she just looked angry but could have also been another indicator (lack of eye contact, red eyes, inattention, and lethargy are also hallmarks of marijuana use). Taking these together, it could be argued that the cop suspected pot smoking and was trying to establish more evidence of it. However during the video of the arrest the cop never once mentioned anything about marijuana; it would seem that if he suspected that at the time of arrest, he'd have told the officers searching her car to specifically look for some evidence of marijuana usage. Hence why I have more questions than answers about the arrest. (for those questioning the legit of the arresting video, you should watch the
full 48-miute video and not just an edited version that they released for news outlets, for I saw nothing that would even suggest that it isn't legit).