I feel no closeness ?

You probably feel horrible feeling this way towards your husbands sister. Its understandable that you could feel like you had no say in the matter of her adoption and being expected to all of a sudden look after this child that you care nothing for. I suggest you speak to your husband about this. You must remember most of her actions are because of her condition. Maybe if you spent time with her, did some enriching activities? It could brighten up both your lives and maybe you can develop a bond with her. I'm no expert, but this is maybe a good starting point.