I am absolutely convinced that the dsd has abandonment issues which need addressed
I was raised by my grandmother with very little contact with my birth mother and was abandoned by my birth father
I definately longed for a baby to fill that gap, without a doubt. Now I didn't get pregnant as a teenager and in fact was a married 27 year old when I had my firstborn.
Well I was not prepared for my emotional response. The birth of my ds sent me reeling into depression as childhood issues came flooding back to me.I found it difficult to bond and the realities of motherhood overwhelmed me. It was not this magical cure for all my childhood sadnesses I had expected.
Fast forward and it has been a happy ending. I had extensive counselling and treatment. I did bond with my ds and adapted to motherhood. I now have a lovely dd and there were no problems after her birth
I am waffling a bit but I do think your dsd may experience a massive fallout when this baby is born. You will not only be possibly helping with childcare but also a very vulnerable girl who is trying to face up to the very real issue of what happened with her own mother.
I don't know the answer to this really tricky situation op and I think you are handling it so well but I would strongly urge counselling for dsd before the birth if she keeps it and of course for yourself as well. This is so difficult for you and of course dsd.