。
Her hat was blown away by the wind.
Literal
She [topic-は] hat [object-を] wind [by-で] was-blown-away.
This is the adversative passive — she is the topic and experiencer adversely affected by the event, even though she's not the direct object of 飛ばす. The construction frames the hat-blowing as something that happened *to her,* one of the most distinctive features of Japanese passive voice.