allthingswillpass I have had another thought and maybe the others who know about this and are reading will come on and fill in if I have missed a point!
Sometimes children do not attach equally to both parents at the same time. Sometimes the attachment comes first to one and then through that to the other. In that it does not mean attaching to you will mean she will fail to attach to DH but quite the opposite, in fact if she fails to attach to you it will make it much harder to attach to DH.
When you say 'I don't support LO behaviour' it sounds like you think this behaviour may be planned or calculated in some way, like a child who plays one parent off against another to get a better present or to get the answer they want if they need to get permission to do something. You may not mean this at all so of course apologies if I have got it wrong.
I think her behaviour is very normal for a child who has been placed with a family and who has had less than three months there to get used to the adults.
I think, allthingswillpass, that you are a teacher with a lot of experience of working with kids, which is great, and does mean you know what it is like in classroom settings. In the classroom I would imagine it is all very equal, teachers do not show favourites and children would not probably be encouraged to always want to be with a favourite teacher etc.
Also in a standard family we might try and say we all love each other equally, no favourites and parents try and love all their children as much as each other however they came to be in the family. This is indeed something to be desired.
However, for your little one she is in a new situation and finding her feet. in my opinion she must be allowed to express how she feels so she will not learn to stifle how she feels in order to please adults or others. Although we all have to do a degree of people pleasing when we are older (to get on in life) as children I believe they do need to learn to understand how they feel, achnowledge how they feel and be able to say how they feel about things really. It is important to have those feelings acknowledged. The love will come; I am sure, if he is patient and lets her learn to love him in her own time.
This article is fascinating and talks about adoption through the eyes of the child. I found it a total eye opener.
www.a4everfamily.org/index.php?option=com_content&task=view&id=53&Itemid=77
All best wishes, I am sure you are doing a great job and you will all get there sometime!