。
She polished off the dish without leaving a scrap.
Literal
She [topic-は] that dish [object-を] cleanly polished-off.
たいらげる (平らげる) means to eat up completely, finish off without leaving anything — literally 'to flatten' something, evoking the image of an empty plate. Common in casual or admiring contexts: a hungry diner, a small child clearing their plate, or someone making short work of a generous serving. きれいに ('cleanly') with eating means 'completely, leaving nothing behind' — the same adverb that means 'beautifully' or 'tidily' elsewhere. Cleaning one's plate is a quietly approved act in Japan, tied to traditions of mottainai (avoiding waste) and respect for the cook.