Maria Thins
Maria Thins( c. 1593 – 27 December 1680) was the mother- in- law of Johannes Vermeer and a member of the Gouda Thins family.
Priscilla Pointer
Priscilla Marie Pointer( born May 18, 1924) is an American stage, film and television character actress.
She began her career in the theater, including productions on Broadway.
Later, Pointer moved to Hollywood to act in films and on television.
She is the mother of Amy Irving, therefore making her the former mother- in- law of filmmakers Steven Spielberg and Bruno Barreto and the mother- in- law of documentary filmmaker Kenneth Bowser, Jr.
Prince Augustus Frederick, Duke of Sussex
Prince Augustus Frederick, Duke of Sussex, (27 January 1773 – 21 April 1843) was the sixth son and ninth child of King George III and his queen consort, Charlotte of Mecklenburg-Strelitz.
He was the only surviving son of George III who did not pursue an army or navy career.
He was known for his liberal views, which included reform of Parliament, abolition of the slave trade, Catholic emancipation, and the removal of existing civil restrictions on Jews and dissenters.
Doria Ragland
Doria L. Ragland( born September 2, 1956) is the mother of Meghan, Duchess of Sussex, the mother- in- law of Prince Harry, and the maternal grandmother of Archie Mountbatten- Windsor, who is seventh in line to the British throne.
She is a former makeup artist, business owner, yoga instructor, and former social worker who worked in the mental health sector from 2015 to 2018.
Marian Shields Robinson
Marian Lois Robinson( née Shields; born July 29, 1937) is the mother of Michelle Obama, former First Lady of the United States, and Craig Robinson, a basketball executive, and the mother- in- law of former U.S. President Barack Obama.
Eldon Howard
Eldon Howard was a British screenwriter.
She was the mother- in- law of Edward J. Danziger and wrote a number of the screenplays for films by his company Danziger Productions.
Cornelia (mother of the Gracchi)
Cornelia( c. 190s – c. 115 BC) was the second daughter of Publius Cornelius Scipio Africanus, the hero of the Second Punic War, and Aemilia Paulla.
She is remembered as a prototypical example of a virtuous Roman woman.
She was the mother of the Gracchi brothers, and the mother- in- law of Scipio Aemilianus.
Vera Miletić
Vera Miletić (Serbian Cyrillic: Вера Милетић; 8 March 1920 – 7 September 1944) was a Serbian student and soldier.
She was notable for being the mother of Mira Marković, posthumously making her the mother-in-law of Serbian president Slobodan Milošević.
Maria Teresa Felicitas d'Este
Maria Teresa Felicitas d'Este (October 6, 1726 – April 30, 1754) was born a princess of Modena and was by marriage the Duchess of Penthièvre.
She was the mother-in-law of Philippe Égalité and thus grandmother to the future Louis-Philippe of France.
Cecilia Underwood, 1st Duchess of Inverness
Cecilia Underwood, 1st Duchess of Inverness (born Lady Cecilia Letitia Gore; – 1 August 1873) was a mistress of Prince Augustus Frederick, Duke of Sussex (sixth son of King George III).
Despite marrying, their union was in contravention of the Royal Marriages Act 1772 and as such was considered legally void.
Consequently, she could not be styled either as the Duchess of Sussex nor a Princess.
She was created Duchess of Inverness, in her own right, by Queen Victoria, on 10 April 1840.

Question: Who is the mother-in-law of Cecilia Underwood, 1St Duchess Of Inverness?