> I don't think anyone knows for sure who did the bowdlerizing

I now see that David Fowler (p. 301 note 15) quotes a manuscript comment by Kittredge, who attributed the inaccurate copying of "Willie's Lady" and the bowdlerizing of "Clark Colven" to William Fraser Tytler, which would mean that he (WFT) is the one who actually made the copy that was used by Child. Rieuwerts just describes it as belonging to him.