Some women (often subconsciously) do that as a test of your manhood. They seldom want an indecisive, wishy washy man. They want you to be firm about deciding that shit, and if you are all limp-wristed about it, she'll lose a measure of respect for you, and start doubting if she really wants to be with you. Of course, that won't happen overnight, but if she sees a pattern of wishy washiness, good luck hanging onto that woman after that point.

The right answer: "Lemme show you this awesome Chinese (Or Mexican, or whatever...) place I know. You'll love it!" If she's not down, she'll say so. More than likely though, she'll be happy she has a dude who can take charge.