It is also possible (although I don't think likely) that the name was Stewart, written as Stuibhard in Gaelic, and was badly mangled when forced into English by some less-than-sympathetic English-speaking civil servant lo those many years ago... that at least might explain grannie's indicating "Stewart" as the clan tartan.

So it looks as if you have three choices for the name "Stobie":

1: Stewart (due to a misspelling); 2: Stobo (a variant on a place name); 3: Variant of Storie, a sept of Ogilvie.

Unless your wife's rotten uncle has a change of heart you may never know...

UNLESS

...you sit down with a couple of Scottish telephone directories, look up the name (Stobie) in widely separated cities (Glasgow, Aberdeen, and Inverness) and write to some of these folks and ask them about their clan affiliation. It is amazing how many people will take the time to reply to a letter from overseas.

ONE MORE THOUGHT was Stobie your wife's grandmother's maiden, or married, name? If it was her married name, might her maiden name have been ... Stewart?