She looked as if to say, "what on earth is that sound?!"
She had this look on her face like, "What is that sound?!"
ご質問ありがとうございます。
① "She looked as if to say,"＝「彼女は～と言うように見えた」
" 'What on earth is that sound?!' "＝「あの音は何？！」
② "She had this look on her face like,"＝「彼女は～のような顔をしていた」
" 'What is that sound?!' "＝「あの音は何？！」
☆"What on earth is ~ "は "What is ~"よりも驚いた感情を強く表しています。
ご参考に。
アメリカ合衆国 
