I think people like this lady act (and think) like they do because they are absolutely terrified of COVID and their lack of control (oddly enough). So their response is to deny it. There is no COVID there is no pandemic, there is np point in being vaccinated or tested - because they are terrified they do exist and they will get it.
It is like people who do not take disquieting symptoms to the doctor because they think they may have cancer, and are too scared to be rational and think that if it is cancer the sooner it is diagnosed the greater the chance of surviving it.
Sorry doesn't answer the problem, but people like this are the most difficult to shift because they are in total denial because their mind is gripped by fear.