@Dtb-Florida0 why would you block dates for guests who haven't paid yet? You are losing on potential bookings. When guests book the dates are blocked automatically. Select the dates, click "edit" and next "available".
Why was your guest unable to make her second payment. Did she not have enough funds?
If your guest wants to rebook, then she should be liaising with Airbnb to resolve this issue.
If you want to keep the original booking, speak to Airbnb and find out whether the guest has now made the payment and ask them how the booking can be reinstated.
If the guest can't pay then open up your calendar again.