When the wall gets busted down she's there, held, and crying: it's clear that the information about the secret training came from her. Harry isn't aware that she was magically compelled to talk until Snape reveals it after his own capture, and evidently he doesn't imagine until that point that Umbrage would go beyond mundane questioning (which is perhaps a bit naive, given he already knows she'll use torture as punishment, but he is only 15 and doesn't realize he's in a film).

So what goes down in the book between Harry and Cho? I don't mind spoilers but feel free to send email if you're worried that your other readers do.