Please help identify this children's movie?

[blueroses]

I'm searching for this 80's (possibly early 90's) animated children's movie involving a princess. Actually this is for a friend of mine and sadly she can't remember
all the details but this is what I know:

-The princess is under some kind of spell and she cannot leave the castle. She has dark hair. There is either a song or a music box melody
that she hums all the time.

-There's an evil wizard who wants to marry her (of course)

-This film might have appeared on the channel called Nickelodeon so it's probably either from the US or Canada.

-This is NOT Beauty and the Beast or The Swan Princess or Labyrinth.

Any help would be much appreciated. I'd actually like to see this movie too. Sounds interesting.

~Rachel