。
She asked a very good question.
Literal
She [topic-は] very good question [object-を] did.
質問をする ('to do a question') is the standard frame for asking — the noun-plus-する structure where 質問 carries the meaning and する supplies the grammar. Compare 質問する (one fused word) versus 質問をする (separable, allowing modification of the noun directly): adding modifiers like よい works smoothly in the separable form.