Why is she a vegetarian?
Tell her you picked up a new hobby of hunting. That'll get her goin' quick.....
Seriously, there have been studies that plants actually do have "feelings". I don't have a direct link to one, but I have seen this before. If you scold a plant all the time it will wilt, not grow as fast, or flourish like a normal plant. Also, you could say trees bleed when they are cut. That kind of stuff. But I think the whole argument is silly, just do what you like.
I think you really need to talk to your wife about it. I mean tell her that is your child too and you don't want her to be a vegetarian. If you wife wants to be one that's up to her, and you don't that's up to you. But you need to find a compromise between the two. Like 3 nights a week she has meat and the 4 nights a week she has salad or whatever. In other words, create a menu for daughter to make you both, and your daughter, happy.
BTW, I'm NOT a vegetarian......
Good Luck!!