Thanks everyone for your interest in helping! Yogiwick; No the barn owner doesn't always add water because, again she doesn't think ahead and upgrade her watering system to "farmer's faucets" that don't freeze. And your right, it is the bigger problem.
Saddlebag; If I don't go out and take care of the waters myself she simply has whoever is doing it make a small hole in the center (not removing any ice) and then it refreezes in an uneven pattern, the next day same thing. So, the walls get thicker and the hole gets smaller, with no water added.
Corporal; your right, that should be part of the job, but again, she doesn't do what is normal or expected.
Verona1016; that is a clever idea, and reasonable in cost. I am not sure if my girls wouldn't consider it a toy and/or try to eat it. I might give it a try, although I have noticed that the sides of the tubs also freeze so it my only work for a short while.
I did find a solution similar on line that I implemented in a pinch. I am using little plastic balls to float on top (they had suggested like a football, but I didn't have that handy) and it keeps a whole open when they push on it. It only works for a little while as the ice get's thicker it isn't effective as they freeze within it. However, they do make it easier to break the ice as they offer some "give" and then a hole to work with.
Thanks again for all the great ideas!