Do not worry at all..your mother will get her extension approved (they do ask for medicals if the applicant has previously not undergone medical exam). cic must have sent you details how to do the medical in the message. the cost of medical exam is approximately 250 dollars and it is not covered in insurance.
Follow these steps to undergo a medical exam:-
Step 1) you need an appointment first from an approved doctor.
Only Panel Physicians approved by Citizenship and Immigration Canada can do this exam. you can find the list of approved doctors from this link
http://www.cic.gc.ca/pp-md/pp-list.aspx
you can call for appointment to the nearest doctor where you live from the above link. (
best to choose a doctor who give you an early appointment ). Also check with the doctor's office when you book your appointment about
e-medical (if the doctor work with CIC via the E-medical). e-medical exams are use to record and send Immigration Medical Exam (IME) results to CIC. It is more accurate, convenient and faster than paper-based processing.
Step 2) one the appointment day. take your mother's passport, identity and the medical request email with you (or your application submission receipt/confirmation which ever has the application file number)
Step 3) on the completion of the medical the doctor will give you a paper having your mother's details and IME number etc..its sort of confirmation of medical exam.
Step 4) scan the document and upload it into your mycic account.
Thats All...you are done and you will soon get the approval and enjoy the stay with your mother.
Hope it helps...