The assumption you make in questioning other people waiting is that they will be behind a car tha may suddenly be put in reverse. For me waiting does not mean I am sat anywhere near their bumper, nor will I be sat in the middle of the road if I have parked cars on my left. There are other options to sitting on the bumper when not proceeding straight through. I might hang back a few lengths or over take it without entering the park so I come at the park entrance at an angle where I am far more likely to be seen. Cannot say for certain unless I was there.
The main point I was trying to make was that a car in the middle of a gateway half on/off a pavement is probably not going to stay in that position long despite the hazards. People can argue that hazards means it is not going to move but the car position says otherwise, and with the driver in the car with the engine on I am not assuming anything. In my opinion the fact that it did move was not some freak occurrence that couldn't be anticipated but a very likely scenario.
Not victim bashing as suggested by another poster as the driver is clearly at fault, Sara was blameless IMO and have said that before.