Taking a step back from this, you have to ask "how could this have happened?"
Chances are that her original contract lets Disney do this. I wouldn't be surprised if she signed away the rights (for sequels and merchandise) to the movie's characters to Disney/Pixar in her contract. Several years ago, Disney dangled the fact that they could release crappy Toy Story sequels over Pixar when they were renegotiating the renewal of their deal.
In fact, I doubt this movie would have been made had she not signed away those rights, and I assume her lawyer let her know what the real-world implications of that would have been.
In other words, I don't know how she couldn't have seen this coming. While she might have assumed the best in Disney, she had a small part in letting this happen.