This phrase generally means that a widow had more legal powers if she stayed single than if she married after her husband's death. Back when a husband controlled his wife's property, a second husband could have done whatever he wanted with his wife's real estate--including selling it.
But as long as the widow remained single--she dictated what happened with the farm. Often her deceased husband would give her a life estate in that property and that she lost it if she married. One purpose this served was that any "new" husband's would not get control of the wife's real estate.