When looking in the International Genealogical Index on the familysearch website, there are alot of Isabella Ross'. Certainly was a common name. The 1841 and 1851 census list her as being born in Ross & Cromarty. The 1861 and 1871 census list her birthplace as Inverness. Plus, on the censuses, her age fluctuates: 25, 36, 44, 50. Not always a clean 10 year difference.
But, I find this christening interesting: Isobele Ross, christened March 9, 1815 in Inverness, Inverness-shire, Scotland, to parents William Ross and Mary Mathison.
Alexander and Christina named one of thier children Christina Matheson MacLeod.
The LDS has a good microfilm to check. #990660, baptisms and marriages from 1715-1854 in Urquhart & Logie. If you have a Mormon church nearby with a family history center inside, you should consider visiting, and ordering the microfilm from the main LDS church in Salt Lake City. It will cost $5.50.