"Can we please stop talking about fish? I need you to tell me where he is, or where you saw him last."

And, well. She actually does pause for a bit, and even entertains feigning some ridiculous reaction just to prove that she can-- but she doesn't want to seem childish, and she's frustrated enough by this whole conversation that she refuses to stoop that low, tempting as it is. Instead she opts to just very deliberately ignore the request, as if that's any less petty of her.