Isabel, you're a star! Your help is very much appreciated, so glad I can now put this to rest! I'm going to contact Stonehaven Heritage, as you suggested, and see whether they might have any pictures they would share.
Thanks to everyone who's contributed to this thread, I've learned a lot about Dunnottar House, which has led me to get to know the surrounding area better too, so now I can appreciate my ancestors' lives more.
I wouldn't want to cause any problems with copyright by posting the pic in here. If anyone else is interested in seeing the house, send me a pm with your email addy and I'll forward a copy to you, with due gratitude to Isabel for finding it

Lass x