It's not that the whole army was trying to rape her. It was clearly one guy and then another guy was pissed at the rapist for interfering with her beheading and tried to stop him. Then it devolved into a fist fight with a few people and a lot of gawkers. The only unrealistic thing was that no superior walked by and broke up the fight and got things orderly again.
But then, maybe she wasn't considered important enough and everyone was just considering a good show. The fact that she kept herself alive for that length of time is impressive.
Honestly, I just hope the rapist gets punished. He was disobeying orders and started a fight. An army can't function well if soldiers like that are left to their own devices. Time to make him an example...