。
She was surprised and made a blank face.
Literal
She [topic-は] being-surprised, [blank-きょとんと] did face [object-を] made.
Two beautifully specific bits of vocabulary collide here. きょとん is a 擬態語 (state mimetic) for that wide-eyed, slightly slack-jawed blankness one shows when caught off guard — neither hostile nor amused, just stunned. 顔をする ('to make a face') is the standard frame for facial expressions: 怒った顔をする ('make an angry face'), 困った顔をする ('make a troubled face'). The combination きょとんとした顔をした paints a precise visual: the moment of being suddenly caught off-guard.