Eastside Cannery would be easier to negotiate because it's significantly smaller. The casino, while good-sized at 62,000 sq. ft, is slightly less than half the size of the Orleans.
I would say that because the most distant hotel room at EC is far less distant than the most distant room at Orleans, that EC could be easier for her. But you could completely eliminate EC's advantage by getting an Orleans room that is close to the elevator and electing not to wander the distant reaches of the Orleans' casino.
Even with mobility issues, I'd strongly recommend Orleans over EC for most every Vegas visitor.