Armstrong tells us (1904, p.72) that the harp was purchased at auction in Dublin by a poor woman. Petrie got it off her, and then after realising the Kildare connection, he presented it to the 4th Duke of Leinster (the head of the Fitzgerald of Kildare family) in 1849, and the harp was subsequently on display for many years at Kilkea Castle.
The harp was at some point acquired by the National Museum of Ireland (the instrument bears the ref. no. 47.1946). Armstrong’s photo of c. 1904 shows it with many broken strings; it is now fitted with a full set of copper wire strings. I do not know of any record of when the strings were replaced, or any measurements or details of the old strings which were on in when Armstrong saw it.