This is hard, at first I thought it couldn't be Cindy, Aurora, Belle or Rapunzel, because they spent most of their lives not being princesses, but Cindy was obviously not happy in A Twist In Time, so... If not Cinderella, than maybe Ariel.

Or Ariel. They both love their families so much that it would be devastating to them.

Cinderella looked unhappy in the sequel whereas Rapunzel can be happy as long as she's with her family.

i cant see her living another life than a royal one

Or Jasmine or maybe Ariel.. Hmm..

Or Ariel.

Or Jasmine or Ariel

Only because she's the only one who didn't really explicitly almost give it up before...

Finding out she's not the lost princess after all would be devastating for her. Where is Tiana? And Pocahontas and Mulan? Mm, if you mean princess as within the story and not the DP status, it's true Mulan has no place here, but neither do Belle or Cinderella.