。
She gave a look that practically said 'get out.'
Literal
She [topic-は] get-out [as if to say-とばかりの] facial-expression did.
とばかりの is a striking expression meaning 'as if to say' — the unspoken message is packed into a facial expression rather than words. 出て行け is the imperative of 出て行く (to get out/leave), making the implied message a blunt command. 顔つきをする (to make a facial expression) treats the expression as something deliberately performed. The whole construction captures non-verbal communication — her face said everything her mouth didn't.