In the United Kingdom, the widow of a peer may continue to use the style she had during her husband's lifetime, e.g. "Countess of Loamshire", provided that his successor, if any, 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". (In any case she would continue to be called "Lady Loamshire".)
Dowager Queen is used in the United Kingdom and several other countries.
In The Princess Diaries books, Mia's grandmother is the Dowager Princess of Genovia, although she is simply known as "the Queen" in the films.
In the video game Fire Emblem: Radiant Dawn for the Nintendo Wii, one can see Ike refer to Lady Almedha as the Dowager Queen of Daein if one can enable the secret conversation regarding Soren in the Epilogue.