As Mocha said, an oatmeal shampoo is great. For a puppy, I'd make sure to have a puppy formula because it will be gentle and more importantly tearless. German Shepherds are nicknamed German "Shedders" for a reason, they're always going to throw off a lot of hair. That being said, it can be minimized with a good oatmeal shampoo (I also like to use a conditioner when possible), a high quality food, an omega fatty acid supplement (one from a plant source like flax in your case), and a good brushing every few days. In a hot climate, she's going to throw off a lot more hair than usual. I get it all the time in Texas. I've heard many different explanations and I'm not sure what's true and what's rumor, but I do know that all of my dogs tend to shed much more heavily when they are living in a consistently hot climate.
Also know that shepherds will "blow" their coats or lose pretty much all of their undercoat at certain points. Puppies will blow their puppy coat when their adult coat starts coming in, and as adults they'll blow their undercoat once or twice a year. So if she suddenly starts shedding really heavily for a couple weeks, don't worry! She is most likely just blowing her coat.