I've read that simply changing food will provoke shedding in some dogs. You may be setting up a vicious circle when it's simply time for her to shed anyway. With mine I do notice that shed time varies from year to year and the intensity varies too. If the food is otherwise working fine I'd be inclined to just brush and vacuum more.
That said I do rotate three foods for my Lab. A change does not make him shed and none of the foods resolves his dry, harsh coat by itself. I supplement with EFAs to improve his coat with all three foods.
A consideration; is the heat on in your house? Is your house properly humidified? Could be your culprit and not the food at all.