That's incredibly stressful @Lauren3359, but it's your property, not Airbnb's, so it's up to you to take control of it. Yes, you gave an inch and they took a mile, and that's the lesson. When you texted and said you would add the pet fee, the guest took it that you had no problem with her doing what she did, and extended that thought to you having no problem with her doing anything she wanted to do. Every interaction with a guest is in some way a negotiation and you gave her power in this negotiation. As hosts we need to demonstrate that we are in control.
You can shorten the reservation and tell them it's over, refund them for the nights not used and get them out of there. You can't sit around expecting Airbnb to police your property. That's your job.