These "problems" you speak of were not helped by Rosie's or that other girls' comments; they just added fuel to the fire. Their comments made them look like ass-holes that will use a tragedy for their own gain. Doubly so when she quits Twitter for another social network. It takes little to no thought trying to link a tragedy to broader issues like mental illness, gun control, poverty, radicalism, religion, etc. These are complex issues that don't have a single root cause.
Vandalizing a campaign sign, building, calling people a "bitch", or making death death threats also takes no thought just like posting in ALL CAPS! Just messing with you there...
I agree that it is
not okay to do these things, but if you choose to be a self-righteous bully like Kevin O'Leary, Bill O'Reilly or even the Fords on social media then don't be surprised if people bully you back. Rosie is not new to the media game so she should know a lot better. Maybe the other girl is just naive, but she's made controversial remarks before.
The internet is the great equalizer in that way. You're free to say whatever garbage comes to mind, but so is everyone else.