In regards XXXXX XXXXX donor money, the best thing to do would be to contact the donors (I know there is a lot) and ask them to redesignate the funds. If the donors designated that the monies be used for a specific purpose and did not, you have a legal obligation to contact them asking them to redesignate or to return the funds. You cannot legally keep the money to pay for admin or other program expenses with donor restricted funds.
Since the money from both Maddie's Fund and Petsmart Charities are grants, verify that the money from the grants were used in accordance to the grant agreement. If the grants were specific to the Mason Creek rescued dogs and you didn't use all the funds, look in the grant agreement. It should specify how to handle unused funds. If you contact them and explain the situation, they may allow you to keep the money to help other dogs. Just be upfront and honest.