The Tin Princess is the analogue of the Tin Woodsman, except here she was born Princess of the Winkies. She was cursed as a child, however, that she would fall apart. As she did, she was replaced by metal until she was fully made of the stuff (alternatively, I've been thinking of calling her the Platinum Princess, as it would be a more appropriate metal for royalty). Not sure about the source of the curse yet, because I haven't settled what to do with the Witches yet.

Perhaps in your fic she was a princess who spurned him, causing his to lose his courage?