I don't think there can be a "right" spelling for proper nouns in traditional songs, for 2 reasons: 1, There were no standardized spellings at the time the songs were written, and 2, there are variants in the way names were sung.
Also there are no fixed names for some songs, people just use a phrase from the song. There's a Carter song which I've seen as either "My Barque of Life" or "You've Been a Friend to Me," for example.
Finally, there may be typos in the title, so sometimes you can find a song via an unusual phrase in the song. I agree -- the shorter the better on search phrases, and try several spellings.
Yeah, Susan, "bonnie" is spelled "bony" lots of places. I have that spelling in two books in the song "Silver Tassie" or "My bony Mary" by Robert Burns. Here "bony" is pronounced "bon-nie" and means "pretty," not "skinny."
Jean Redpath and Helen Schneyer both sing "Bonnie Susie C." I don't know whether Helen recorded it. Maybe Sandy Paton could tell us.