This is Marguerite Countess of Blessington. I've no information about who engraved this portrait, which was done sometime in the 1830s. She wrote a number of novels and poems, and edited several monthly journals, for one of which this picture was done. She was a famous beauty -- her best known portrait, by Thomas Lawrence, is in the Wallace Collection on London and can be seen on Wikipedia -- and was clever, witty and charming. But though she married a wealthy earl, her early years as a kept mistress had ruined her reputation, which suffered even more in later years owing to her long relationship with her handsome son-in-law, Count Alfred d'Orsay.