Hello Sarah,
I’m so sorry to read about your experience. I think everyone in this forum would benefit on knowing how this story ended as to know how to proceed if a similar situation happens to us.
Depending on which country you live is whether you are legally allowed to touch your guest's stuff or not. What I'm not really sure is how long did she overstay. Was it just a few hours or was it days? What I would have done, if it had been hours, would be to message her through Airbnb, probably she's at the hospital or somewhere without access to the phone, make it really clear that this is not okay but you're cutting her some slack.
Depending on the time of the day, if it's noon or in the early evening, I would welcome the new guests, receive their stuff and explain the situation, even maybe offering to stay at your place (where you live) while the guest checks-out where they originally booked.
I think everyone's reaction is valid as it is a reflection of their own experiences. No one is too harsh or mellow. And also, as I mentioned before, it would really depend on how long ago was the suppose check-out.
Please fill us in!