While the information about the husband may not always be directly related to your research on the wife's family, the paperwork the widow filed may mention her date and place of marriage and even include testimony from those who knew her before her marriage or who were at her marriage. Frequently these people are biological relatives of the wife. And those are people in whom you are interested.
It's even possible that your ancestor provided a statement in his or her sister's widow's pension application.
So look at those aunts of your ancestor--did any of them apply for a widow's pension?