。
She was wearing a new hat.
Literal
She [topic-は] new hat [object-を] was-wearing.
かぶる is the specific verb for wearing things on the head — hats, helmets, wigs. Japanese uses different verbs for different body zones: 着る (upper body), 履く (lower body/feet), かぶる (head), かける (glasses), はめる (rings/gloves). The ~ていた indicates she was wearing it at a particular past moment.