Sometimes, using the cortisone for a week will completely clear up the rash and give the skin a chance to rest so it doesn't continue to react. You might also try stopping the cortisone more gradually because there can be a rebound effect. But if the rash keeps coming back in that one spot, I would suspect contact dermatitis. Does she sleep on that side of her face? Or have a snuggly she rubs there? You might try using "free and clear" laundry soap and absolutely no fabric softeners, dryer sheets or bleach. The dryer sheets are particularly allergenic because the oils from the sheets leave a residue on the dryer drum and are re-released on subsequent loads.
Since you mention the dry arms and legs, it sounds like your baby may have sensitive skin in general. She may be allergic to a number of items, both in foods and in her environment. You will have to be the detective to try to pinpoint the cause of the rash. This is easier said than done so good luck.