"So much for free speech."
Actually, Bush's joking comment is a great example of her right to free speech. However, her employer no doubt has certain rules that she needs to follow.
And regardless of her "setting an example" for the kids, from a safety standpoint I don't think it wise to have a bus driver that flips off other people that annoy her. One would hope that another angry motorist would not take out their road rage on a school bus whose driver flipped them off, but you never know.
BTW - Seattle, although known for politeness in shops, etc. has a greater than average incidence of road rage.
But that gesture is as integral to driving as the turn signal!