Presumably her first name isn't on record. According to this she was a daughter of Duncan Stewart 5th of Appin.
https://sites.rootsweb.com/~rykbrown/stewart_of_invernahyle.htm#Ale... Stewart 4th of Invernahyle
That would make her a distant cousin of her husband.
Link broke. Try again
https://sites.rootsweb.com/~rykbrown/stewart_of_invernahyle.htm#Ale...
Apparently her father was a grandson of this one
Duncan Stewart, younger of Appin