Parenting a securely attached birth child is completely different from parenting an adopted child and I, and Safia, have both. Also bonding and attachment are not the same thing.
when you are pregnant the child begins to get to know the sound of Mummy's voice and the sound of her heartbeat. As your tummy grows Mummy also begins to bond and attach with the child. After the birth, Mummy becomes fine tuned to the voice of her baby and will attend to it's every need. Baby cries - mummy picks it up, checks to see if it needs a clean nappy/food/a cuddle. Baby relaxes because mummy has attended to it's needs. Baby cries - mummy responses - baby relaxes - baby cries - mummy responds - baby relaxes - and on and on the cycle goes and baby learns that it can trust mummy because mummy is always there. Baby bonds with mummy - loves her and also securely attaches to Mummy - trusts her. As the baby gets older it is able to deal with separation - in the way that Lettice has described above - because the baby knowsthat mummy will always come back because that is what she has always done. So mummy has put the ground work in to begin with and the child has learnt that mummy will come back because s/he is now securely attached to her.
An adopted child has had that cycle of bonding and attaching broken -and maybe more than once. If the child has spent any time at home with the birth mother and she has not attended to it's needs when it has cried, the baby learns that mummy cannot be trusted especially when she completely disappears after the child is removed and placed with foster carers. Foster carers may be good but will not be able to attend to the child's every need - they may have to take the child to contact meetings were they have to hand the child over to a social worker who then waits for "birth mum" to show up (if she does). Foster carer is not allowed to stay during contact meetings - so child has no secure base. child is constantly being left with strangers /other members of the foster carer- foster carer will also have meetings to attend with her own social worker which will increase when prospective adopters are found. Introductions begin with prospective adopters - new MUMMY and DADDY. Introductions take place may be over one or two weeks during which time , foster carer begins to leave the child with the new strangers more and more until one day the child is taken to a strange home and the foster carers also "disappear". Another "attachment" figure has disappeared. Child has learnt that people, especially "Mummies" cannot be trusted - they always leave you and will not attend to your needs.
So you leaving your daughter at nursery is only reinforcing what she already thinks about mummies - they leave you, don't attend to your needs and disappear. She cries at nursery and you walk away.
You need to stick to her like glue - every time she cries YOU need to respond and start to re-create that cycle of bonding and attachment. You in effect have to re-parent her - and as she has already had that cycle broken twice it will be even harder for her to start to attach to you - start to learn to trust you. Some children are so badly damaged by their experience that they are never able to securely attach to their adoptive parents - and end up with avoidant/anxious/ambivalent attachment styles leading to all sorts of problems as they get older.
This is why you need to take her out of nursery and keep her at home with you. Being an adoptive parent is not easy I know and it is a very intensive way to parent but if you want to give your daughter the best chance of securely attaching to both you and your husband, then you have to do it.
best wishes xx