@Simon758How long did your guest book
As @Branka-and-Silvia0 said, this is directly from the Terms of Service that your guest agreed to by booking your listing through Airbnb:
8.2 Booking Accommodations
8.2.1 You understand that a confirmed booking of an Accommodation (“Accommodation Booking”) is a limited license granted to you by the Host to enter, occupy and use the Accommodation for the duration of your stay, during which time the Host (only where and to the extent permitted by applicable law) retains the right to re-enter the Accommodation, in accordance with your agreement with the Host.
8.2.2 You agree to leave the Accommodation no later than the checkout time that the Host specifies in the Listing or such other time as mutually agreed upon between you and the Host. If you stay past the agreed upon checkout time without the Host's consent (“Overstay”), you no longer have a license to stay in the Accommodation and the Host is entitled to make you leave in a manner consistent with applicable law. In addition, you agree to pay, if requested by the Host, for each twenty-four (24) hour period (or any portion thereof) that you Overstay, an additional nightly fee of up to two (2) times the average nightly Listing Fee originally paid by you to cover the inconvenience suffered by the Host, plus all applicable Guest Fees, Taxes, and any legal expenses incurred by the Host to make you leave (collectively, "Overstay Fees"). Overstay Fees for late checkouts on the checkout date that do not impact upcoming bookings may be limited to the additional costs incurred by the Host as a result of such Overstay. If you Overstay at an Accommodation, you authorize Airbnb (via Airbnb Payments) to charge you to collect Overstay Fees. A Security Deposit, if required by a Host, may be applied to any Overstay Fees due for a Guest’s Overstay.
Do not let your guest try to fake you out with threats. She is trespassing.
Perhaps send the terms to your guest via the message system, then contact Airbnb to start charging her for the overstay and to begin contacting her to get out. As also suggested, change the locks when she leaves for the day. If she threatens you with legal action, tell her to get busy filing a suit.