City ordinances are one thing, your lease is another, it's a private property you signed a lease and you have to abide by that lease, so if you signed a lease that says no snakes or likely no exotic animals it does not matter what the property manager says, what prevails is the piece of paper that you signed.
As for getting your snake to become an animal therapy too many people are now doing this for the wrong reasons when they start having issues with their landlord for example that is abusing the system IMO, if you needed a therapy animal why didn't you have the paperwork saying so before having issues?