This is what I recall about the book: It was about a young girl whose parents died at sea, when the ship they were sailing on sank during a storm. The young girl is living with a cruel woman whom I believe was a witch.
There was a painting of a sinking ship (depicting the ship the girl's parents had been on board) hanging in their house. The witch owned a chest which the girl was forbidden to open, and she threatened her that if she ever did open it; evil powers of some kind would come out of it.
A little later into the story the girl (who spends most of her time locked up in her room) somehow meets a prince, who falls in love with her and they decide to get married. The witch finds out about their plan, and once again locks the girl up, and decides to marry the prince herself by disguising herself as the girl. She also stripped the girl of all her clothes so that she would not dare to go outside, even if she did get out of her room. The witch leaves the house to marry the prince, dressed in a wedding gown with a vale covering her face. The young girl manages to get out of her room and finally opens the chest and (I think) she finds a quilt or something similar which she wraps around herself. She crashes the wedding and the witch is exposed. There was also mentioned something about black crow feathers sticking out from underneath the witch's wedding gown.
The book was beautifully illustrated, and the story did not stretch over a very large number of pages. I read the book in the middle of the '90s, so it is possible that it was published sometime during that decade, or perhaps during the '80.