I believe

And in the bath today, her mother and I were helping her play with her duck.

"Do you want duckie?" we would say, and offer her the duck.

"Is that for me?  Why thank you for the duck!" we would say when she offered it back to us.

"Here you go," we would say, the one of us to the other, "Would you make sure Sophie gets this duck?"

"Duh!" said Sophie.  "Duh! Duh! Duh!"