The info I have from a pamphlet " Fraserburgh A short guide to the town " tells that Sir Alexander Fraser Lord Saltoun, 15th Laird of Philorth sold it to the Northern Lighthouse Board in 1786. The lighthouse was erected in 1787 by Thomas Smith. Your grandmother quite likely lived in the "castle" but it was probably as part of the lighthouse staff. You may be able to get some information if you email info@lighthousemuseum.org.uk. There is also a website www. lighthousemuseum.org.uk. This info is in a booklet "Aberdeen City and Shire Routes to your North East Roots." North East Scotland's Coastal Trail states Kinnaird Head lighthouse had an unusual birth , having been built on top of a castle. I have to believe what I read!!! Janet in NZ