Is she supposed to say an existing nursery rhyme, or make one up herself? I can think of a jump-rope rhyme related to Cinderella, but I don't know if that would qualify as a nursery rhyme.
Cinderella, dressed in yellow(pronounced yella)
Went downstairs to kiss a fellow(pronounced fella)
By mistake she kissed a snake.
How many doctors did it take?
1,2,3,4...