The Baine remark was said from Sylvanas' point of view though.She was the one who realized that if Baine really wanted it he cud snap her like a twig.Not surprising considering he is a 10 foot,800-1000 pound humanoid of pure muscle,but it still shows her body is not insanely durable.It is probably strong,considering she ripped an animal apart with her bear hands in rage and also tanked a hit from Genn Greymane,but nowhere near something like a Tauren.
However physical endurance may not be enough when dealing with a primal force like the void.In the end it kinda depends on what exactly Alleria can do with the void....