Presuming it's clear up front in your listing your hot tub isn't working and the garden is shared, I'd just confirm to the guest she chose the non refundable option in return for a lower price.
screenshot the info in your listing showing the garden shared and send to her.
i would say as a gesture of goodwill on your part if she decides to cancel and you get a replacement booking you will refund the guest fee for any nights you get a replacement booking after any replacement guest stays.
say you will not accept swearing or rude responses because she didn't read the listing description.
report her comments to airbnb
Can't see a reference to a hot tub in your listing ???
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