Now, I'd say she's done her homework and discovered he was an only child.

我得说她倒是煞费苦心发现他是我们的独子。

The girl had done her homework.

这个女人下过一番功夫。

That means he did his homework and it's still done; it's still finished. She has done her homework.

那意味着他完成了他的家庭作业并且仍然完成了；它仍然完成了。她已经完成了作业。