Sorry to hear about your problems with your lease.

IMO, you should check with your state laws, maybe call your local legal
aid, but the majority of the time written agreements override verbal
agreements, especially when it's landlord v tenants, unless you can get
the original owner to state you were allowed to have the ferret.

If you received a "comply or vacate" notice, she is doing this legally.
In the eyes of the law you have violated the *written lease* and its No
Pet clause, no matter how long you have been living there or how many
witnesses you have had to your ferret and no complaints about it.

Good luck!

[Posted in FML 7464]