What was the title of Queen Mary, widow of George V, after her granddaughter became Queen Elizabeth II and her mother Elizabeth became the Queen Mother?

Although she became Queen Mother on the death of her husband George V and the accession of her son Edward VIII (and, following his abdication, George VI) she never used that title and remained Her Majesty Queen Mary until her death in March 1953.

https://en.wikipedia.org/wiki/Mary_of_teck%23Queen_Mother

Queen Elizabeth, wife of George VI, adopted the title "Queen Elizabeth, the Queen Mother" on his death and the accession of her daughter because to have remained simply Queen Elizabeth would have caused confusion. Queen Mary had no such problem.

This site suggests she was for a brief period before her death, "Dowager Queen Mother"
https://en.wikipedia.org/wiki/British_queens_dowager

A queen dowager is the widow of a deceased king. Thus both Queen Mary and Queen Elizabeth were Queens Dowager. Neither of them wished to use that status as a title.

In addition both Queen Mary and Queen Elizabeth were queen mothers as mothers of the monarch; in the case of Queen Mary, George VI whilst he lived and in the case of Queen Elizabeth, Elizabeth II.

The Garter King of Arms' proclamation of the styles and titles of Queen Elizabeth the Queen Mother at her funeral on 9 April 2002 illustrates her dual status as a queen dowager and a queen mother - "the late Most High, Most Mighty and Most Excellent Princess Elizabeth, Queen Dowager and Queen Mother ..." As mentioned, she adopted the status of queen mother as a tile - Queen Elizabeth the Queen Mother - to distinguish herself from her daughter who is also Queen Elizabeth.

"Dowager Queen Mother" does not exist as a title, and I cannot find it in the reference quoted. Once George VI died, Queen Mary ceased to be a queen mother but remained a queen dowager. Her title, Queen Mary, did not change.