My 3 year-old, who has been eating meat his entire life, does not yet question "where meat comes from". For the most part (aside from chicken & turkey), the names of the meat don't necessarily correspond to the animal. He'll ask us "what are we having tonight" and when I say hamburger or ham or beef or pork, its just the name of the dish he's eating. I'm not saying "cow or pig". THAT would definitely make the questions start to fly out of his mouth. He hasn't realized the chicken yet and I must admit I've switched to saying "we're having meat" a few times. So far so good - he hasn't made the connection. I'm hoping for a year or so before that happens! I, too, am dreading it.
I knew where the meat came from when I was young (~4) and I was fine eating meat until the day I was exposed to the entire butchering process with chickens on our farm (when I was 8 or so). After that day, I went several years not eating chicken. So when the day comes that your daughter asks, definitely explain things in simple, more general terms (food chain; some animals are on earth to feed others) but definitely no details. It can be traumatic.