So David and I decided to have a talk with her. We asked her "Riley, who's your best friend", immediately she responded "Peyton!"; so we asked "Can Bosco be your best friend?" and her response was "YEP!". So we asked "Can Daddy be your best friend?" and with the sweetest little grin replied "nope", and when asked "Can Mommy be your best friend?" we again got a "nope".
So... I have no idea where she learned about best friends, but, dog really is man's best friend. Er, Riley's best friend :)

Lucky Dogs!