Give it a try without the foam, it may not need it. If your wife finds it too drafty in the helmet, then just trim the piece of foam and add it to the shield.
There's nothing worse than spending so much dough for a shield/helmet that won't fog up, but end up getting frostbite instead. I had trouble with a helmet I bought last year and ended up sending it back for a refund at the end of the season.