Unless you a professional dog boarder, in which case you *could* charge you customary rate, all you can do is have the estate reimburse you for the actual out-of-pocket costs (for example, dog food) you incur  while caring for this dog. However, since reimbursemen of out-of-pocket expenses incurred in caring for estate property or assets (which includes the dog) is a proper expense, you can at least do this.