Your post is not clear as to what the circumstances are. I have to ask questions. 1) Why did you not know of the proceedings? 2) Do you have a close and nuturing relationship with the sister? 3) Do you know the adoptive parents? 4) Do you maintain a close relationship now and does she want the same thing? 4) Considering the length of time she has been with the adoptive family, what would the change do to her? 5) Is this your desire or your sisters' as well.
As an adoptive mom, I know the strain it can put on a child's mind. When considering a permanent change in one's life, especially a child, you have think long term. Your sister may well have adjusted to her new family and her mental state may be very healthy. I feel that if you had a very close contact with your sister you would have known the circumstances and been able to speak during the proceedings. Before disrupting a child's world do some self search and make decisions wise for all involved. The adoptive parents have something to loose too as well as it may be the desire of your sister to stay their daughter. There may be a way for all of you to be happy and content together. The decision you make will have to last a life time. Good luck with it and God bless you.
