Change Work and Holiday Visa to Visitor

[Mailovesbubbletea]

Hello!
I used the search button but couldnt find anything to answer my question.

My sister is currently in Toronto on W&H and her visa is expired end of August. I want to visit her first week of September and we are going to the States the week after. As we are from Germany we dont need a Visitor Visa (up to 90 days). Does she need to change her W & H into a visitor visa? Would it be possible to go to the border and re entry as a visitor?

Thanks

Mailovesbubbletea