@Denise1145 I'd say it's better for the guest to cancel from her end using the EC- she'll have to provide some documentation that the road is closed- perhaps you might send her something that would make it easier for her?
If you agree to issue full refund, then Airbnb could apply penalties for a host cancellation- you could contact them to make sure this won't happen if you choose to go that route.
This is a grey-area cancellation- she can't get to your place because of the road closure, so is it a guest initiated cancellation or a host not being able to host a guest? Could other guests get to your place if they were coming from a different place, or is your place not able to be accessed at all right now?
If no one can get to your place from anywhere, that's really a host EC, so in that case, you should follow the procedure for that.
Doesn't sound like it really matters to the guest how it's done, as long as she gets her refund and doesn't have to spend too much time on it.