I think it could be a couple of things. One, maybe, just maybe teeth are bothering her, but I've never had that happen. More likely, she's just 'gone off her food'. I have a couple of picky eaters and when that happens, I just boil up some white rice, chicken breasts and some carrots and mix maybe 1/2cup in with the kibble with some non-fat, salt-free chicken broth. Usually, if nothing's wrong, pup will gobble that right down. It can be varied with any low fat meat.
Good luck! Puppys really try to make you crazy; it's part of the charm?!!!!