To effectively fix a flea infestation you need to both treat the dog and the environment. Fleas jump on and off the dog and lay eggs on their bed, in the carpet, cracks in the hardwood, etc. If she doesn't have many fleas or hasn't had them for very long, you at least need to wash any beds or bedding she uses in as hot a wash cycle as possible and vacuum areas she hangs out in thoroughly every day for a while. If she has lots of fleas or it's been a very long time, you may need to resort to steam cleaning carpets and furniture and using chemical flea killers.
Dawn will only kill adult fleas on her. It's much more effective to use a long-lasting flea treatment, such as a collar or the liquid you put between shoulder blades. These will continue killing new fleas as they hatch. There's also products like Capstar that very effectively kill almost all the adult fleas on your pet very quickly, but will not continue to kill newly hatched fleas, so you usually need to combine them with a long-lasting preventative as well. Every furry pet you own should be treated, because if one has fleas, they probably all do.
Go for a high quality brand with a good reputation, and never cheap out. Hartz brand, for example, is notorious for selling products that have given animals serious chemical burns when used correctly. Some have even died. These products are still on the shelves for some awful reason. Look for brand names like Frontline, Seresto (they do collars), Advantage, Bravecto, etc. that have excellent safety records and are vet-recommended, and make sure you buy the correct version for her size and use them as directed only. You can ask your vet what they recommend, because some areas are starting to see fleas become resistant to certain treatments, and because some treatments aren't recommended for households with cats (if you have any).
