。
She was wearing a cute hat.
Literal
She [topic-は] cute hat [object-を] was-wearing.
かぶる is the head-specific wearing verb, distinct from 着る (torso), 履く (lower body), する (accessories), and かける (hooked-over items). The ~ていた form expresses the past-ongoing state: she was in the state of wearing the hat at some past time. かわいい hats are a fashion mainstay across age groups — from 麦わら帽子 (straw sun hats) to ベレー帽 (berets) to the elaborately frilled hats popular in アイドル fashion.