Emma is Princess Emma. She is not the prince from Sleeping Beauty because Regina made a reference to her when she spoke to Maleficent. From the way that conversation went it sounded like Snow and Sleeping Beauty are two different people and two separate stories. Besides Charming only put the egg into Mal as a dragon and Emma killed her as a dragon after the curse and after Regina and Mal “talked”. Emma could still be the Swan Princess, wasn’t her name Emma too?