does she need a visa?

If she holds a valid Green Card ( I - 551) then she does not need a visa to travel to Canada.

If she holds a valid Green Card ( I - 551) then she does not need a visa to travel to Canada.

But, interestingly, the reverse is not true - permanent residents (landed immigrants) of Canada still require a visa to travel to the United States unless they are citizens of a visa waiver country or are otherwise exempted.

As others said, no visa required. For future reference, Delta has a tool that lets you enter nationality and the country of permanent residence to determine travel requirements.

http://www.delta.com/planning_reservations/plan_flight/international_travel_information/visa_passport_information/index.jsp