I assumed that Daru does not know that Amane is his daughter, because he says

And then talks about how it sounds like a fantasy; this implies that Okabe had just told him that Amane was his daughter for the first time.
Either that or I'm interpreting it wrong.
It's been a while since that episode where the time machine is repaired.
And I thought that he sent a d-mail to prevent the time machines from breaking due to rain, and therefore Amane is not injured by the misrepaired time machine.