The technicalities of a 6 months visa! Please advise!

Just a quick question: My mother has a 5 year multiple entry visa. Each time she comes here she stays for 6 months.

I was wondering: If we go to Costa Rica or Cuba for a week in December (which we do every year), can she stay for another 6 months in Canada after our arrival from holidays?

This way, she could stay for roughly 6 months before our trip to Cuba/Costa Rica and another 6 months after our arrival from holidays. A total of some 12 months with a break of 7 days in-between the first 6 months and the second 6 months. Someone advised me that as long as she leaves Canada after 6 months, even if it is only for a week, she can stay for another period of 6 months.
I know that I would have to make some arrangements for her medical insurance. At any rate, we want to do everything legally as I am in the process of sponsoring her here.
Kindly advise.
Thank you so much!