Need to terminate an employee who has cancelled the in-person meeting, claiming she is too ill and under a doctor''s care.

Yes. Mail is better. Remember that, under the Americans With Disabilities Act (if it applies to your business), you may have a duty to provide a "reasonable accommodation" to an employee who is still capable of performing the functions of the job. Nothing prevents you from terminating an employee who is unable to perform the job functions with a reasonable accommodation.