You say the child was 'listed' and 'the government knew about her'. But she was not examined. What does this mean exactly? Did your husband include the fact he had a child on his forms, but explain that the mother would not let her be examined? If this is the case, usually the government demands several times that one gets the child examined, and if the immigrant insists that it is not possible, the government has the immigrant sign a statement saying he understands by not having the child examined he knows that he will never be able to sponsor her in the future. Did your husband sign such a document?
If he did, there is no chance to sponsor her. Humanitarian and compassionate grounds only work when a person is a member of the family class, and by not having her examined, she is excluded from the family class.
However, occasionally the visa officer processing the file will say you don't have to have the child examined. If this occurred, then it is possible to sponsor her.