You can try scenting with bedding. Make sure all other conditions are ideal. At night, make sure the rat is hot enough, make sure there's no distractions (like a TV on in the background). If necessary you can also try braining. It's a little gross in concept, but it's not hard. Also, don't try too often to get her to feed. If she skips one, wait until the next appropriate feeding day. I don't recommend going live until it's a last resort because they can get stuck and be picky and refuse f/t after that.