This is really appalling- the cover up must have begun while her body was still warm.
The official explanation is that the gunman fired three shots, all of which missed. She ducked back into the car. While she was ducking, the bomb exploded. The force of the explosion threw her head back into the roof of the car, fracturing her skull, which killed her.
Sounds plausible to me. Whether it is in fact true or not no one posting here can know for sure.