In England, bishops are not Most Reverend as they are in the Irish Empire; in their natural modesty Anglobishops are merely Right Reverend (unless they are Metropolitan Archbishops, when they do get a bit moster). And Benedictine abbesses by Tradition have precisely the same dignity as a diocesan bishop. "The Right Reverend the Lady Abbess of A" precisely parallels "The Right Reverend the Lord Bishop of B".
For completeness, I will add that fully professed Benedictine Choir nuns have in England historically had the title Dame (= Domina), just as Benedictine monks are Dom (= Domnus = Dominus). In Medieval England, 'Dame' was often used for the wives of knights or noblemen. In modern England, the style Dame is now used as the equivalent of Sir ... you talk about X having received his knighthood or Y having got her damehood. I wonder if the British Establishment asked permission from the Order of S Benedict before usurping their title in this rather cheeky way.
And now the United States of North America are to have their own Right Reverend Lady Abbess ... thought to be first ever. At Gower in Missouri, next Monday, Mother Caecilia, hitherto Prioress, will be blessed as an Abbess , and some of her sisters will be professed. This will complete a fantastic weekend in which the brand new Abbey Church of our Lady of Ephesus will have been consecrated. Sancta Maria, Regina Apostolorum, ora pro eis, ora pro nobis, ora pro Ecclesia Dei adflicta.
I hope on Sunday to offer a few words about the Rite of Consecration of an Abbess in the Tridentine Pontifical.