While watching the movie, sweet memories of the days in the forest with her father were brought to mind.
【正确答案】：While she was watching the movie, sweet memories of the days in the forest with her father were brought to mind.
【题目解析】：句子的主语是sweet memories，而从句中 watching the movie的主语实际上是she，所以she不能省略，必须以she作为从句的主语。
