Regarding property managers vs. property owners?

Is a rental property owner legally obligated to abide by an agreement signed by a property manager he/she hired to manage the property?

The story: My family moved in to a rental home three years ago. At the time, we were told by the manager that no pets were allowed, but that the owner had agreed to consider a pet after we had established ourselves as reliable renters. After three years of paying rent on time, I approached the property manager about the possibility of having a small bird (e.g. a cockatiel). We were told that we could not have a bird, but that we could have a small dog. We began looking for a dog and found one six months later. I introduced the dog to the property manager, signed a pet agreement and paid a pet deposit.

The owner is now claiming that she never okayed a dog. She's waivering back and forth about the dog, and accusing us (not the property manager) of trying to take advantage of her. My question is: isn't the already-signed pet agreement legally binding? The owner does have a signed agreement with the property manager giving her the legal right to sign leases, etc. in lieu of her. We have never violated any terms of our lease, and would never have adopted a pet had we not had advance permission.