The Frog Prince

I read "The Frog prince". 
A princess has dropped a ball on a lake. A frog appears there and　he said that I'll get you a ball if you'll become my friend and allow me enter the castle.
She promised so then, but when a frog will get her a ball, a princess has broken her appointment easily and has returned to a castle.
But when a princess was having a meal with her father in a castle, the frog came to castle....
Reading this story, I thought I didn't like the princess. I thought she is a frivolous woman.