AutumR: ~~~As an adoptee I must say, this is far more complicated than dealing with a rebellious teen.
Some adopted children feel betrayed when they learn of their adoption from someone other than their parents. It hurts to learn that something soooo personal about you is known by others,something you yourself didn't know.And worse, is that the people you love are "hiding" it from you. It makes you feel as if there's something wrong with you.
Yes,most teens rebel, but this secret could be making the situation harder for both of them. She needs to tell her daughter. Sometimes there is never going to be a right time or place, but it must be done.
Best of luck to your friends.
Good advice.
I also think it is not the message, it is the deliverance of the message.
If the mother approaches her daughter, then she may rebel even more and refuse to deal with it. Who knows?
I know how a child I know has dealt with it and it was nothing short of amazing to meet his brith mother and feel loved, his adoptive parents supported him hugely when he requested to meet his birth mother.