Dog after first month of lease?

A tenant was clearly stated they do not have a dog and do not plan one. They said their existing puppy dog they do not plan to bring.

and just after move in on first month they got a dog which is 50-60 lb. Now lady says it is a service dog and not a lease violation. She refuse to do pet application or pet fee or monthly pet fee. She says by law she can keep service dog.

Is it a violation or can they keep service dog without pet fee or application?