@Emily1053 The terms of payment are between Airbnb and the guest, not the guest and the host. Your guest's (a complete stranger to you at this point) finances are not your problem nor your affair. If she can't afford to pay for her booking on time, then she'll lose the booking.
You really don't need guests like this.
Just tell her that Airbnb deals with the payment process , not hosts, and that she'll have to contact Airbnb.