The child is probably very anxious and lonely. She probably is not sure of her position in family, maybe feels threatened by a new addition to family and is worried sick about her mother. Probably meeting her mother once she is shifted to ward, and giving her more attention, and involving her in baby care will help her. Meanwhile keep up her nutrition with semisolids, milk, soups, juices, cereals etc. Consult a counselor if need be. Take care!