I've heard of these cases before, and the problem is usually pretty straightforward. They're simply not bringing her out when she really needs to go, and they're bringing her inside the house when she does have to go.

30 minutes just isn't enough for some dogs. For example, I had to stand outside with Ivy for almost 2 hours before she did her first potty outside. Additionally, do they play with the dog when outside? Tell them not to pay attention to the dog and not to play with it when outside until the dog eliminates. As soon as the dog eliminates outside (it will eventually!), praise to the high heavens and initiate play. Also, do they keep their dog on lead when outside? How about when inside? In the beginning, it's best to "tether" the pup to the caretaker to ensure that there are no accidents. It also helps for bonding

Hope that helps you some. In most cases, unless the dog has a medical problem, it's simply a case of wrong timing and misunderstood reinforcements.