It is hard to hear of the death of a family member, friend or acquaintance. You realise it is important to send your sympathy to the family, especially the widow. If you have little experience with this, you'll need to know how to address the sympathy card when mailing one to the widow. It is important to acknowledge her correctly and observe proper etiquette. A widow is trying to deal with deep grief and accept the fact that her husband is truly gone. She is still very much his wife and will want to be addressed as such.
Address the envelope to "Mrs. John Smith" or "Ms. Sarah Smith." Sarah is the widow of John, so when using Mrs. you will use the deceased husband's name.
Address the envelope for a newly widowed doctor as Dr. Sarah Smith.
Address the envelope to a newly widowed woman who is a minister as Reverend Sarah or Pastor Sarah Smith.
Write a personal note inside of the card to a newly widowed woman that you are an acquaintance of by addressing her as Mrs., Dr. or Reverend Smith.
Write a personal note to a family member or friend and address her as you normally would, Aunt Sarah or Sarah. The outer envelope still must read Mrs. John or Ms. Sarah Smith.
Do not use the widow's maiden name unless she has used that as her name after getting married.