First of all, this problem is not unique and can be caused by several possible things including not bathing/rinsing her correctly so please don't take insult if I detail this for you. Wet the dog thoroughly, then shampoo with a Medicated canine shampoo (Pyoban will help open pores, or use Malaseb or Chlorhexidine 4% to fight bacterial and fungal problems, or even try a human dandruff shampoo once like Selsun Blue)and lather twice if needed to get a good lather on the dog. Let stand on the skin for 10-15 minutes, and then rinse the dog very well. Then rinse a second time, very well, to be sure you have ALL the soap off the dog. You can then 'rinse' the dog with an apple cider vinegar solution (1 cup vinegar & 2 cups water). The cider vinegar is to discourage fungal growth.
Do this 2 or 3 times a week for 1-2 weeks until you see some improvement, then drop back to weekly and continue weekly for the rest of the summer or until cool weather. Just one medicated shampoo is not enough to bring about the change you are looking for.
Because it also sounds like the dog has 'dry skin' and that contributes to shedding, you need to add some oils to his diet...but there are good oils, and there are excellent oils. If you add one teasp of olive or veggie oil to his dinner, that should help some (not too much or it will give him diarrhea). If you purchase a good Salmon OIL rich in Omega Acids that would be much better for his overall health including shedding. There are several good brands available at online pet supply companies like Entirelypets.com or Drsfostersmith.com and they usually come with a pump-dispenser top so you use one pump per evening meal. There are also fish oil capsules. The least expensive way to buy those is at Costco or WalMart in the human vitamin section. Again, some of the online pet supply companies have canine oil capsules that may...may...be better...can't say for sure because I don't use them.