http://www.hooyou.com/adoption/faq.html
http://www.uscis.gov/adoption/immigration-through-adoption/other-adoption-related-immigration
If she's not an orphan, she will definitely NOT get a green card immediately. Non-orphan foreign adoption requires the parent adopt the child, and live with the child for two years before they can apply a green card for her. Usually a "real adoption" happens before the whole family moves to US, so the requirement would be easily satisfied.
However, in your case, since the adoption happens now, there are two years requirement for your family and the niece to live together before she can apply for green card based on the adoption. Either your family moves back to China to live with her for two years, or she find some other visa (F-1, J-1 exchange student) to come to US to live with you for two years.
Your hu*****and needs to talk to an immigration lawyer. And you need to talk to an estate lawyer, because if you dies, the child will inherit your money. Of course if you don't agree, adoption cannot happen.
