@Mike-And-Jane0 with all due respect, regardless of any written house rules, if a host and homeowner asks a guest to wear a mask (in the middle of a pandemic), the guest should comply. It's common courtesy as well as a health mandate and respectful.
If @Michelle2746 didn't include that in her house rules that's not the best thing, but bottom line it's completely disrespectful of the guest in so many ways, and she should not have allowed them to stay. Aside from which I believe that AirBnB is still mandating mask wearing in common areas. Both hosts and guests agree to that, I believe.
Enforcement is a different matter....