"Unless Grandma wants to take apart that whole coat just go with a windbreaker under it. You can also find windshirts that may fit better under the wool coat.
If you decide to go with resewing the coat you can find some lightweight windproof nylon or nylon taffeta that will work for a lining. But...
You'd better offer to take the coat apart for Grandma, that's the really hard part. Sewing it back together is far easier."
X2.
Achigan, yes and no. The warmth isn't lost, but yes, it is warmer with the shell outside. Inside though, you can wear another wool layer and have great freedom of movement, as opposed to wool on wool which tends to bind some with the friction. It also retains the quietness of wool with the liner inside, as well as the camo effect.