I read something once that said that when a puppy does this, they feel dominated. It is the feeling of having something OVER or ON TOP OF them that they dislike... Not so much the clothing. My Lucy does this - that stock-still, immobilized, stare-at-the-ground-with-her-head-down, so-pathetic-looking-it's-sad, POUT - when I put her rain coat on her. At first I thought it was just the raincoat... But it turns out to be anything with a hood.
I honestly have no idea how to fix it... But if I can find that book, it might help you to understand WHY she does this. And that can't hurt! So, if I'm able to find it, I'll let you know!!!