السلامُ عليكُم و رحمة الله و بَركاتُه 

There’s a sister who took an oath saying that she wouldn’t watch any movies or TV shows anymore. However at school they have watched movies during school (some were related to the school topic, some were not). The sister didn’t know what to do so she just remained in the classroom while they were watching the movies and watched it with the others…

Is her oath broken? Does she have to expiate for it?