I am sorry you had this bad experience .
Im sure you've already familiarising yourself with Airbnb's service animal policy but here's my summary .
If you homeshare and have a medical condition that means pet hair triggers allergies you don't have to accept service animals . @Krista-and-Steve0
I have an exemption because I am asthmatic. (I provided evidence from my doctor).
if the guest told you it was an emotional support pet you didn't have to accept the animal.
if the guest declared it was a service animal you can ask which tasks the animal helps the guest with and confirm as a service animal it must be with the owner at all times .
as you don't live at the listing as you are hyper allergic I suggest you get a cleaning service to go in and clean the property and do an extra charge to the guest for deep cleaning on the deck.
an honest review will help warn your fellow hosts.