Yesterday I stumbled upon a family tree that supports her position.
John Doyle- Irish cartoonist- begat Richard and Charles Doyle- both of them distinuguished graphic artists- and Charles Doyle begat Arthur Conan Doyle, creator of Sherlock Holmes.
What I'd say to her, if she ever found out about the Doyles, is that instances of artistic gifts manifesting in three generations of the same family are vanishingly rare. Can you think of another? I can't.