。
She glanced at his face.
Literal
She [topic-は] his [genitive-の] face [object-を] glancingly looked.
The fleeting-glance pattern ちらりと見る — a 擬態語 (state mimetic) + adverbial と attached to the verb of looking. Note that 顔をちらりと見る is a more focused phrasing than just 彼をちらりと見る ('glanced at him'), zooming in on the face as the specific target.