Thank you Stellenbosch. I did end up calling them (before I saw your message) and their direction was that if my outside camera didn't show her leaving this morning that I could knock on her door, but not enter the room. Then contact them and they would give it one hour past the check out time and do something. What they would do, I don't know. My biggest concern was that my guest was okay and not sick (or worse). I wanted to send her a message, but not be intrusive. What I ended up doing is to send a message thru the ABnB app, asking if she planned on taking an evening shower (she had done that on her first night here), so that I could turn up the water heater which is colder at night. She responded to that, so I knew she was okay.