So if she is just Visiting? Whats the issue?
US Citizen's are allowed to visit for up to 6 months.
If your true question is can she quit her job, moved out of US residence, cut of the majority of ties with the USA, move her things to Canada, establish herself here in hopes of getting PR status?
The officers at the POE don't take kindly to these types of "Visitors"
She must be able to prove that she is a visitor to Canada at each and every entry into Canada. If she can't she may find herself in trouble.
She will be returning to NY state monthly to visit with her son and family.
Not an encouraging statement.