A up armoured vehicle would also not have protected them, i have photos of a VBED that hit a Dyncorp convoy in Herat in 2008, the car is toast.
Keep in mind, that they are speculating that she was in a car, that crashed into the SUV/ bus, with a force of that explosion it destroyed everything in the death acre ( doods akker). This was planned and executed with military precision. Look at the photos on news24.
The VBED's carry massive amounts of explosives and it is not the bang that kills, but more the force of the blast, that kills on impact.