How to protect myself from litigation.
You stated that one of your pet-sitting business rules is that the animals are fixed yet the cat was accepted for boarding without being fixed. A contract can be as simple as authorizing a specific person or entity to have an animal (description included) neutered by a licensed veterinarian although there are other provisions that a pet-sitting business/boarding facility or individual should consider to include in a pet-sitting/boarding contract, such as a hold harmless clause which addresses liability, animal care, which may address such things as emergencies where the animal may need veterinary attention, failure of the animal’s “parent” to retrieve the animal when scheduled to do so, etc. Consider having an attorney review your contracts and/or draft contracts for your business. I also suggest procuring insurance if you do not have it.