How ironic that the OP says that its sad the BIL doesn't pay DSD enough attention when the child's own biological dad won't even allow her to live with him and his new family. How ironic that the OP says that her DSD is very insecure because her BM yet no mention about the insecurity from her dad's, OP's DH, actions and feelings.
I am not a parent nor a step-parent but a person can't help but read this little girl's situation and feel incredible sadness for her because the two people who are suppose to protect and love her, her parents, have let her down. Stories like these rests on my mind. I don't know who the OP is or her DSD but the little girl compels me and makes me want to say a prayer for her even though I am not religious at all.
I guess I have to give credit to BIL and SIL for stepping up to the plate when her dad and mum, and social services failed her or she would still be back in the revolving door of foster care. But it makes me wonder what will happen to this almost 12 year-old and her future.
I wonder if she will end up back in foster care now that BIL/SIL have their own kid and her Dad won't take full responsibility for her. The OP has given them an out because of her reasons for not taking DSD when she was just 8 years-old. Is the DSD trying to bond with the OP in the hopes that one day she can live with her dad and half-siblings? Or will she always be on the outside of both families, not really part of her aunt/uncles and yet not part of her dad, just accepting the scraps of love thrown her way? Will she always be searching for love and acceptance in the wrong crowd/men/friends and turn out like her mother? Or will she be one of the lucky ones who overcome their difficult childhood and unfortunate circumstances to one day have a successful career and family life with a man who will love her and appreciate her?
I wonder if the dad pays his brother maintenance? I wonder if possible, allowing BIL and SIL to adopt her will give a better future. OP says that DSD wants to know why she can't live with her her BM but you have to think that DSD also wonders why she can't live with her Dad. I wonder if and when DSD finally gets the whole sordid story, will stop bonding with the OP because of her decision? Then who will be the adult that she can talk to? Who will be her safety net and rebuild her up again? Will she have built up enough mechanisms to cope with news? News like this should be done with psychologists/counsellors on hand.
I am sorry for the musings but like I said earlier, I don't know this 12 year-old girl (and very much about the whole situation) but from what I do know, her story touched me. I might be a naive fool but I am rooting for her to overcome the odds.