Kayleen,
Let me offer your daughter and her husband something from the other side of the coin that might help.
I was a foster child myself, and although I cannot speak for every foster child out there I can say that good foster parents left thier mark on my heart and my life forever. Nothing can ever take away the good things..period!!!!! No matter what the child goes to from there, the good things given by caring people are like the finest gold, it shines through everything! There may be times when it doesn't seem like it, but the love and caring will never be forgotten...and it will be passed on someday!
I know this to be true because I was every forster parents worst nightmare! I was the monster child/orphan who seemed to have no limits to my ability to be hateful, spiteful, vicious, and just plain cruel. But somehow I turned out ok, ( or so my wife claims) You don't suppose that the people who tried to give me love, caring, and attention made a difference do you?
YER DAMNED RIGHT THEY DID!!!!!!
Tell that young couple that they made a difference and that those words come from one who has been there and done that!
(Someday we'll talk...you might find my experiance interesting)