So I do not think it is stockholm syndrome. As Belle came back because she was trying to save Beast. She didn't have to...she chose to. Two big issues I have with my favorite Disney movie are

1. When she was finding her father...why not just have Beast help bring him to the castle.

2. Why was an 11 year old boy punished for being selfish...he was a brat sure but he was a kid. The enchantress still punished him AND his servants? That is really unreasonable expectations.