Doesnt it annoy when your vegetarian friends...?

First of all, in a non-confrontational way, address your friend and tell her that you respect her, but are frustrated with her criticism. Tell her that biologically speaking,you are an animal too, and you would hate to think that she wouldn't give you the same respect she gives cows and chickens. Also remind her that scientifically speaking, humans are made to be omnivores, just like certain animals are carnivores and eat each other. She doesn't have to agree with you, but she should respect you. Tell her that she's made her point, she doesn't need to make it over and over again on a daily basis.