下面这句话中“while”是从属连词还是并列连词？为什么？

Question

But the stationmaster was adamant: rules could not be broken. And she had to watch that train disappear towards her destination while she was left behind.（但站长态度坚决，规章制度不能破坏，姑娘只得眼看那趟火车消逝在她要去的方向而撇下了她。）——《新概念英语》

Answer 1

while并列连词，意思是：然而，所以这是一个并列句。