Is a forced 2 1/2 lunch "break" legal?

My girlfriend works in a child care center in PA, she is paid hourly (a little over minimum wage) and has been told to take a 2 1/2 lunch after being sent home early on tuesday. Because the owner doesn't want to pay out overtime. In most situations, for lunches, staff can't leave because of ratios. So is there a legal issue here?