It is either ; Turlough O'Carolan (if you want to use his full name ), or just Carolan,(without the " O'") if only using his surname. Something to do with the niceties and conventions of Erse, apparently . No, I don't understand either, but there it is.
       As to the subject matter ; I see no reason why Carolan should NOT have written a piece in honour of a Princess Royal,who could have existed anywhere,at any time,and does not have to have been English-----far from it. If it was written as a" tribute", does this make it a "Pleraca", like that written for Fanni Ni Poer, I wonder ??
             Up until today,I thought it WAS English,but in a way I am pleased to discover that it might not be !!