@Jan186
If the guest already agreed to a pet fee before or during the booking, there's no reason to expect a negative review. But after the stay is complete, you no longer have any leverage if the guest doesn't want to pay.
If you didn't have a prior discussion about pet fees, I don't recommend springing them on the guests now. Your listing doesn't specify extra charges for pets (and appears not to allow pets in general), so if the guest disputed the resolution, Airbnb would most likely decide in their favor and deny the payout.