The fact that others have chickens and or roosters is irrelevant. YOU are the one who has been caught. Other people roll stop signs, speed, and drive drunk all the time too - doesn't provide a defense when you get caught doing it. Zoning is the same way.
Fact is, ESA Abuse is percieved to be widespread. That's the reality. Fact is, you were caught first, and now seek an exception after the fact. That's the reality. Fact is, you want an exception to a generally applicable law based on a piece of legislation which allows self-certification, and as such, receives little respect in the law. Certainly less than objectors claiming First Amendment protections for religious liberty, another place of self-certification. That's the reality.
You will have to overcome all those issues to be successful, and unlike the ADA, ESA doesn't have much "teeth". If you weren't in CA, you'd have almost no chance at all. ...and even there, they worry enough about ESA Abuse to have recently passed legislation seeking to curtail it.
The only things in your favor (apart from the fact that CA will even consider it) is that your granddaughter was previously in treatment - so you aren't appearing with a letter from any of the myriad Internet sites dated after the infraction, and that litigation in your state is so expensive and onerous that its not worth it to most defendants to do more than propound discovery and go thru the motions while seeking to settle.
The Law, it is said, "is an @$$". [with apologies to the BYC Moderators,
its a quote approximately 500 years old, which I have tried to render somewhat less offensive to the very sheltered.] In the eyes of the law, your feelings, and what your neighbors may or may not be doing, are irrelevant. If you want to win your claim, you need to focus on what the law DOES care about and how you can use the legal process to make it a fight the municipality wants to settle guickly and quietly. In the words of Sun Tzu, "Victorious warriors win first and then go to war."
You now have the benefit of my opinion and experience, which, together with $5, might buy you a short coffee at Starbucks. Worth more than an apology, which I won't be offering. Focus on your feelings of hurt, of being singled out, your sense of moral "rightness" and you greatly increase your chances at losing this fight. The LAW does not care. I don't care about those things either, but cared enough to offer a useful guide for proceeding and an overview of the landscape in which you will fight.
As it is unwelcome, I'll be getting a real coffee, and stepping off this thread. Good day to you, madam.