It's possible the cat has died, she's temporarily keeping the pet for someone else, etc., so there is a slim possibility she's not in violation of the lease. Tell the property manager and ask them to investigate the situation. (That's what you pay them for, no?) I'd suggest to the property manager not to tell the tenant how they found out if they don't need to. Make a record of the "ask" for supplies and keep it for your files just in case though. Look up the laws for your state, as to what you can require (e.g., if the tenant+dog stays, a pet fee?) If you don't have restrictions on age of pet, I'm not sure you can complain about it being a puppy specifically.