yes i thought this would not be easy at all, that's why I've probably not heard of anyone else who has done it b4.
also i think it would cost at least 1,000 usd+ for processing fess + other fees, probably also a settlement visa for the child £500+
another option might be to use the European route, as I'm pretty sure a niece would be classed as a family member. you would have to go and live with your wife in another European country for 6 months+, and apply for a family permit for her, but even this is risky, and I'm sure you have to live with her for 6 months....