It's too early to apply for renewal on December 6, 2026 (unless his legal name change). Usually people apply up to 9 months before the expiration date.
Actually you don't need rent a house for living near a lake. I know an affordable lake front hotel (with high speed internet) in Nanaimo, BC which has a shopping mall nearby and great road conditions.
Many grandparents provide gift to their grandchildren too. She will likely need NOA anyways to apply super visa for her parents. It's only August now and has up to the end of the year - 4 months, if she wants to apply for next year. This is also short to mid term plan.
She need to meet the income requirements in order to apply for her parents' super visa. The income doesn't have to be employment income - it can also be investment income. Since other family members are supporting her financially, couldn't they provide funds to her investment account and earn...
At land borders, CBSA officers usually ask if travelers have return tickets. It might be a problem if they don't (from my experience, they never asked to show proof).
According to cbp website, the driver should have a notarized copy of a permission letter addressed to the "Officer in Charge of U.S. Customs and Border Protection" to drive the car across the border.