See link below. If her passport has no specific stamp with a date then she can stay for upto 6 months
https://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=1016&top=16
However it is generally recommended to spend an equal amount of time out of Canada before returning otherwise CBSA may suspect she is trying to live in the country as a visitor. So 6 months in 2 weeks out and return not recommended given worst case refused entry or a shortened visit in weeks.
Of course she could as well get another 6 months but no way to predict anything given depends how convincing she is or not appearing to live in Canada.
For longer stays you can either use the extend stay as a visitor process multiple times until refused (not recommended for long term) or apply for a Super visa from her home country which supports 2 year stays valid upto 10 years.
I am afraid that your family situation will have little influence on entry to Canada with a TRV given it is so common that children leave their parents in home country and is just one of the downsides of immigration.