A possible long shot.
In his 1872 will, Edward Moore Gawn mentions his daughter, Isalen Jane Gawne.
Edward Gawne owned Kentraugh, a 277 acre estate on the coast, south of Colby in the Parish of Rushen.
Per the IGI her christening was June 18 1848.
She appears in the IOM census in Rushen of 1851, 1861 & 1871.
What was the married name of your g grandmother. She can perhaps be found in the 1881 census?