No, unfortunately, there are no standards for this. The matter is dealt with only by the terms of the contract: so if the contract provided that the tenant would be responsible for utility bills that exceeded some maximum amount, then you could hold her liable for the cost of the extra energy. But if the lease simply states that energy is included in the rental and does not cap or limit how much she can use, you have no recourse.Possibly you may wish to see if by replacing any appliances or bulbs with more energy efficient ones, adding insulation, etc., you can cut down on energy bills. Speak with a tax preparer or accountant: you may be able to get some tax advantage for capital investments, and there also may be government or utility subsidies for taking energy-efficient measures.