You should alert AirBnb immediately to the situation. The guest may realize they’re injured and AirBnb likes when you're proactive about alerting them so a case is open already if the guest contacts them.
Not sure why they tripped but if you’re not at fault, which is hard to prove, they’ll tell you to file a claim. The guest will no doubt be peeved and give you a bad review. Depends what you can afford to lose. The guest could also retaliate by asking full refund and also leaving a bad review.
Whatever made her fall, consider measures to prevent it from happening again whether it’s rearranging furniture or adding watch your step stickers and photograph these for your records.
If it’s entirely their fault and they don’t even offer to compensate, then I’d probably mention in the review something like “Some (light/moderate/considerable) damage occurred during her stay which she didn’t offer to cover and we didn’t pursue.” Which is enough to alert future hosts of a hazardous or clumsy person who doesn’t offer to pay for damages.
The Johnsons