If you have trouble finding all of the connections from your wife back to Scotland, as many do, I would suggest searching for the origin of the name and from which clan it sprouted. You have the option of either clan in your case, but if you can't decide I would suggest going with the earliest.

I know that for my heritage, there have been diasporic Todds in Scotland, England, and Ireland for hundreds of years and people argue over whether Todd (Todd, Todde) is a Scottish or English name. But the origins of the name are found in Berwickshire where they were a sept of the Gordons, before spreading across the isles. So I sport the Gordon tartan. Eventually, I might trace my ancestry all the way, but there are these wonderful ink smudges and the lack of universal registries that seem to make that goal a lofty one.