In the Regency, the word dowager was used in newspapers, letters, the Gazette,  and on letters. One was never addressed as a “Dowager.” One does not say, “Good day, Dowager Countess.” The woman is simply addressed as a “Lady So-and-So.”

The word “dowager” eventually began to attract negative emotions, and widows began avoiding the use of the word. However, it was in use in the Regency for widows of landed and usually titled men. Though today, widows prefer not to use Dowager, at the time, a widow of a man of property was a dowager, meaning entitled to “dower,” a widow’s share for life of her husband’s estate.

The grandmother usually became the Dowager Countess of Somewhere as soon as she was widowed. Until the woman’s son marries, it is her prerogative to leave off the Dowager and just be Lady Somewhere.

According to Debrett’s Correct Form:

“Officially the widow of a peer is known as the Dowager Countess (or whatever) of X, unless there is already a dowager peeress of the family still living. In the latter event, the widow of the senior peer of the family retains the title of Dowager for life, and the widow of the junior peer in that family is known by her Christian name, e.g., Mary, Countess of X, until she becomes the senior widow. . . . When the present peer is unmarried, by custom the widow of the late peer continues to call herself as she did when her husband was living, i.e., without the prefix of (a) dowager, or (b) her Christian name. Should the present peer marry, it is usual for the widowed peeress to announce the style by which she wishes to be know in future.” (Titles) This last bit is 20th century, and Black’s agrees: most widows do not use “dowager” at all anymore, and simply use the Mary, Countess of X option, announcing in the press the style they will be using. 

Invitations to court and the lady’s name in the newspaper or on formal lists (as in the list of those who attended a Queen’s birthday bash) would use dowager if there was another  one with her same title. If there was more than one widow, the first widow is the dowager and the others are Mary Countess of X.  The main purpose was to avoid confusion between or among ladies.  One never addressed the lady as a dowager in person. One only spoke of her as the dowager when it was necessary to distinguish her from any other living Countess of Someplace. As a twelve-year-old girl (Think how girls as young as 12 could marry) could actually be a dowager, the term was not connected to age. However, because older women were usually dowagers ( n the upper crust) and people spoke slightingly of sitting among the dowagers and chaperones, the widows decided they did not like the word. If a woman wanted to present her granddaughter at court, or her new daughter-in-law, she would  have to describe herself as a Dowager Countess, for instance. Ordinarily, though, she would not use the term, at all.

Technically, the definition according to the Oxford English Dictionary applies to: “A widow with a title or property derived from her late husband.” As in a widow who has estate or property left to her by her right of dower. In usage, it can be applied to any elder woman of status (a widow who has rank).

The more proper use is that: “…the widow of a peer may continue to use the style she had during her husband’s lifetime, provided that his successor, has no wife to bear the plain title. Otherwise, she more properly prefixes either her forename or the word Dowager, e.g. “Jane, Countess of Loamshire” or “Dowager Countess of Loamshire”. “As with a lot of styling, it is up to the lady to set how she wishes to be addressed: She may not want to become a dowager just yet and so may resist that push.