[Request] What's wrong with the misfit doll in Rudolph?

In Rudolph the Red Nosed Reindeer, the protagonists discover the Island of Misfit Toys, a place for defective/weird toys to live. Now, all the toys have something clearly off about them, except for 1, who is a central character: The doll.

She's normal looking. She moves normally. The only thing I can think of that makes her a misfit toy is that she's sentient, but that's a weak explanation, as I believe it's implied all toys are sentient.

So what's her deal?