I don't think you can extend many times ... only 1-2 before they ask you to leave.I cant stress too much on this issue.
I am going to apply for my mother supervisa in April/May IN SHA ALLAH as her regular visa is expiring in a few months anyway.
I think if IRCC issued her regular visitor's visa two times before then why wouldn't they grant her supervisa this time.
In your case I suggest you keep the same visa as it's valid for 10 years and once your mother is in Canada keep extending her stay as supervisa.