One of our Pekin ducks is having trouble walking. We noticed yesterday that she is not putting much weight on one of her feet. When she walks, she is only stepping on the front of her foot and is holding it up when she is standing. We thought she may have had bumblefoot, but upon inspection, she doesn't have it. Could her leg possibly be broken or sprained? How can we tell? And if so, what can we do about it?