Lots of people egged-on her self-destructive behavior, but lots of others raised the alarm. When she posted her chug video with barleywine/Xanax (or some anti-seizure medication), lots of people told her she should not be mixing those things, but others thought it was funny and definitely rewarded it with attention. When she posted her chug video where she was brandishing a firearm, lots of people said she shouldn't be handling a weapon while intoxicated, but others thought it was awesome.
I don't think that BiL is responsible for her death (I think these behaviors would have happened/were happening independent of BiL), but some people's behavior toward her certainly didn't help. Ultimately, there is only so much you can do for a stranger on the internet though.