answer:Traditional etiquette calls for “Mrs.” Older widows of my acquaintance have preferred that, and it’s not any news to them that their husbands are gone. But fashion in forms of address has changed so much in recent decades that many women might never have chosen to use the traditional form even while their husbands lived. I don’t think you can go wrong with “Ms.,” but your best bet might just be to ask them which form of address they prefer. Some may feel that they’re still Mrs. Smith and always will be, and it would disrespect their late husbands to call them otherwise. Others may have been “Ms. Smith” from the time they were married, and “Ms. Jones” before that—or maybe they never used their husbands’ names at all. I, for one, appreciate your use of the more formal address instead of presumptuously defaulting to first name.