On the other hand, They (these Census takers) would not have been total outsiders/strangers to the community. So it would have been hard for her to make a conviencing lie. Because, they would have not only have taken her word, but they would have checked her statement with her neighbors, if they had reason to suspect it.
However, why are we assuming that she was lying?
If her husband died in Camp Morton in 1863, AND she knew it, is it possible by 1866 she had remarried and your research has not been able to confirm that? It would have been quite hard to have hidden her husbands death from the community that late, a year after the surrenders. In general men who had not returned home by late 1865, within 6 months of Prisoners of War being released in June of 1865, were not going to return at all. Men who had served with him, and maybe who had even been in prison with him, would have come home with the news, usually. Many widows pension application were accompanied and approved, on no more documantation than the statement of men who said they had served with the widows husband, even if they hadn't.