I think Charolette liked Wilbur because he was not scared of her when everyone else wanted no communication with her. Also, because he wanted a friend and neither of them had any, so it would make sense for them to be friends. Plus, I think because Wilbur was so nice to everyone, Charolette (most likely) was thinking he would want to talk to her and become her friend. That is why I think Charolette liked Wilbur so much.