2 weeks ago my guy was like this as well. considering his size (and getting bigger still) totally unacceptable behavior. he's had training as well. I bought a prong collar and a traffic leash, which is just a very short leash. if you opt for a prong collar make sure you watch some vids on youtube about how to use it properly. with the shorter leash it would be impossible for her to get 6+ feet in front and just want to take off. concentrate on keeping her head/shoulders around your own legs when you walk, and don't walk quickly! walk your own pace. it will probably be awful at first but my guy has already gotten way better.
another thing I tried was with food he (obviously!) gets excited. he used to run to his feeding spot but whenever he did I started saying NO and returning to the kitchen to start over. these days he'll walk, still excited, next to me. no leash, nothing. but he gets that he's not to race past me, but walk by my side. I'm really impressed because he's doing this even when he's so excited about his food.
hope some of this helps! look at it as a challenge
edit - I'll add that between regular collar and prong I tried a choke collar but he pulled anyway until his breathing was ragged. Think other GSD's are like this too. For some reason they don't mind choking themselves out but they don't like the pinch of the prongs