Hello STudent

You have not mention in your question what are the certificate courses your grandmother have  made choice. At her age 81 most of the courses is not  fit for her. The following are the certificate courses which may be helpful to to fulfill her interest of short time courses-

Certificate course in yoga_1 month and 15 days course_qualification HS

Certificate course of Buddhist study_6 month course qualification 10 + 2

Certificate course in library and information science 6 months course qualification 10 + 2

Certificate course in social work 6 month course qualification10 + 2

Certificate course in advanced Indian history 6 month course, qualification 10 + 2

Certificate course in ideal son thoughts of Dr Ambedkar  6 months course qualification 10 + 2

Certificate course in clinical psychology course duration 6 months qualification 10 + 2

The above mentioned courses may be fitted for her to continue and help for best time spending option.

Hope this helps.