They didn't occur around the White House, the US Capitol, and the National Mall.
They also usually end when cornered by the police, and the driver doesn't drive away -- twice -- injuring officers in the process.
The point is this woman was not armed, did not have a bomb and never even drove through barrycades. She had no chance of getting anywhere near Obama. She was probably terrified by a bunch of roided up cops screaming and pointing guns at her so she tried to flee.
If you are buying into this myth that its OK to shoot anybody getting near government buildings you need to re-think.