Hartz is really bad for dogs and cats. Millions of adverse reactions have been reported from people using that crap. They've been trying to get Hartz off the shelves for years. Do a google search and watch for anything weird with your dog. And using flea shampoo is bad period because of the chemicals...mixing it with Hartz would be even worse.
Along with the garlick..Try a couple of drops of Tea Tree oil on her..... It's supposed to repel them. Also add like a teaspoon of Braggs Organic Apple Cider Vinegar to her food and then mix some with water and spray it on her. A few drops of tea tree oil on her fur could also help repel them.