For her, they are 'worldly children'; children who are most likely will never become a Witness, and so why even consider opening one's heart to them and their suffering.
All children are 'worldly children' - before their parents indoctrinate them into being Jehovah's witnesses...Muslims....Catholics...Hindu's...Jews...etc
You could try and say that to her?
Although there is a strong chance if you adopted kids she would teach them to become JWs in short order!
I'm really sorry that your impulse to do good is thwarted by that cold hearted greedy religion. It's a shame, too, because I've read it's the one main regret many childless witnesses have, although these days it's not explicitly prohibited.
It's good though that you can see past your wife's behaviour as being not of her own doing. Perhaps if you try and encourage her to do non witnessy things and just generally enjoy yourselves together? Show her how great being a family could be by taking her places families frequent? Just some ideas, anyway. I really do feel for you because you found the witnesses uncharitable nature always one of the worst aspects of their belief system even when I believed it myself.