Beatrice de Stafford, Lady Ros of Helmsley - Courtesy titles

I know little about the lady in question, but seeing that she was married firstly to a baron, secondly to a knight, and finally to an earl, and courtesy titles (unless lost, such as through divorce) are always rendered with the highest title first, her display name should be "Beatrice FitzGerald, Countess of Desmond". The only exception to this would be if she possessed a higher title herself, which does not seem to be the case here. She was thrice widowed and did not remarry after her final husband the Earl died, so "countess" is the title she deserves.