I have seen stuff like this before, and I though I would give it a go. Its not very 'pink princess like' but my daughter loves it all the same. My niece lives with me as well, so I probably end up making another one so their not fighting over it.
I just took an old box cut it up to fit on of my daughters larger/taller barbies (some are shorter, like the tinker bell dolls) hot glued all the pieces together then took some old pieces of fabric and cut them to fit over the head and foot board. then took the same fabric for the sheet. made the pillow, which I glued onto the bed so she wouldn't lose it. Then cut some old lace for the bed skirt. And Ta da! Cinderella is already napping.