So I tend to understand the aggravation of the author. But, it feels like an over-reaction here (though it may be the article's tone). I didn't feel outraged despite the article and comments here expecting/demanding me to be.

I had to look hard at the picture. Looks like they threw Merida in the bathtub, and put her in a nice dress and eye-color for the "ball." But, when the Princesses get together that's how they get dressed up, for a party, no? Evening wear is expected and appropriate in that situation. Is Merida supposed to show up for the Oscars in riding-chaps and bow?

If this is the only representation of Merida from now on, I'd agree with the anger. But, even tomboys would dress up for a ball, even if they felt a bit itchy. They would get a lot of compliments too. That's how the world works, folks. Men have to fit into expectations too--the suit/tuxedo is ridiculous at < 35 degrees latitude.

So, I feel no outrage for her to have a bit of range. From the fox-hunt to the royal ball. Even if she'd be a bit uncomfortable, we all have obligations to society.