Final answer:
The Fairy Godmother is sorry because she made a mistake in her statement.
Step-by-step explanation:
The Fairy Godmother is sorry because she made a mistake in her statement. In the context of the quote, the Fairy Godmother is expressing her regret for wrongly identifying the creatures. She is not sorry for being happy, sad, or for any positive memory. Therefore, option (a) The Fairy Godmother is sorry for being happy is incorrect.