Hi Kristin
I think it is very good of you that you are trying to help your guest in any way you can, which I'm sure most of us hosts endeavour to do, however, if it is going to put you under stress to be able to pay your bills and feed your family and it is within the cancelation policy that you and the guest agreed to within the Air BnB platform, then you shouldn't feel that you have to refund 100%.
A guest receiving a 50% refund for their cancelled stay is much more than the airlines and other accommodations are offering and this should not send the guest into financial hardship. However, Air BnB forcing hosts to give up 100% of their income WILL put hosts into financial hardship.
If Air BnB stood by their cancelation policies that the host and guest agreed to then I believe that is the fairest on both parties. The host should be able to limp by on half of their income and the guest, by all rights, should claim through their travel insurance. If a guest chooses not to take out insurance as a traveller, then the host should not be forced to pay for that.
We are frequent travellers ourselves with a family of five and we have yearly travel insurance and it is worth every penny. I then don't have to feel guilty about asking innocent ma and pa parties ie Air BnB hosts like you and me to pay me money from their bank accounts.
I know I am ranting slightly here, but it is a very frustrating situation to be in.
All the best with your guests, and lets hope this virus gets under control sooner rather than later!