The news report about a visit by Chinese vice president to the Netherlands said 会见威廉—亚历山大时，韩正首先转达了习近平主席和彭丽媛教授对国王和王后的亲切问候和良好祝愿 As far as I know, only PhD is used to address a respectable person, Dr. So and So, other titles are not heard of. First Lady Peng is better known as a singer in China much earlier before her husband's presidency of the country about 11 years ago. Also, I notice this is the first time 教授 is added to the name of the first lady on official occassions. When and how is it to be used properly? If her title is not 教授 but 主任医师 or 高级工程师, is it still OK to be used this way?
教授 (professor)is a formal address, a title for a teacher who teaches at the university level. They have to be at least a Ph.D. or above.
As long as 彭丽媛 once taught in a university, people can address her as 彭丽媛教授, unless she has another title with higher honor. For example, Dr. Jill Biden is also the First Lady, people can address her as Dr.Jill Biden or First Lady Jill Biden depending on which title they consider more important