Factual clarity may never be achieved. The eyewitness accounts seem to be muddled and inconsistent, and certainly there is an anti-Israel agenda at work to some extent or another. The important thing is moral clarity. Is CS tear gas only used by rogue states or is it widely used by normal countries for riot control? If it is a legitimate tool for riot control, then I don't see why we should not accept the assertions that Abu Rahmah was at least peripherally present at the demonstration and that her final round of symptoms started with some kind of exposure to the gas. So what? A person who wants to live in maximum safety should not participate in weekly demonstrations that often turn violent.
Some explanation seems to be in order no matter who we believe in this case. Deaths from outdoor exposure to CS tear gas appear to range from extremely rare to unheard-of. There must be some reason that Abu Rahmah died when nobody else even needed gas-related medical treatment. We may never know what it was. Maybe the doctors were incompetent, maybe she was more sickly than her family is admitting, maybe she had some rare predisposition that decided to express itself just at that moment. A narrative which mostly consists of an IDF soldier firing something and a nonviolent protester dying is very exciting and useful to anti-Israel propagandists. However, a great many legitimate activities lead to an occasional death: skydiving, riot-control, marketing snacks containing peanuts. Let the would-be activist beware. He is not entitled to more than the proverbial buyer.