@Donna480
Be careful with this one! Airbnb will always try to cajole you into refunding, even where no refund is due ("do the right thing" is the phrase most commonly used by CX agents in such instances)
As per Airbnb T&Cs, a guest is automatically issued a refund under the Extenuating Circumstances policy, when the guest has a "medical emergency", so the fact that they're even consulting you about it would lead me to believe that the guest has provided no supporting documentation, but they're trying to pressure/sweet-talk you into refunding anyway.
If you really want to be nice about it, you can offer to refund if - and only if - you receive a replacement booking of equal value, and even then, only after you've been paid for the replacement booking. Or you could just advise Airbnb to tell the guest to claim it from her own travel insurance.