Hi first of all wish you all the best and fast recovery for your mom.
My mom took the visa on time. She was approved. I actually submitted everything they ask. Cant remember details since its been couple years ago. But one importsnt thing is to show them that she is cured ni matter what is the operation. She must be healthy to travel. Any pre-existing condtion that is cured is normal to them. They already know moms and dads or grandparents are old and they expect health conditions ao dont worry.. you can call the doctor who is hired by the canadian embassy in your country backhome to ask them about there diagnose if she could pass this part which is the most important. And let the doctor know how much you miss your mom.
Plus dont forget the insurance company must be legit in canada and get a good expensive one and you can cancel after she get approved and get a cheaper one. Depends on your budget and needs. Good luck and hopefully i answered your question