Can Camilla Duchess of Cornwall become Queen?

As wife of Charles... she could. She won't, though; it was announced prior to their marriage that if/when Charles ascended to the throne, she would take the style and title of Her Royal Highness The Princess Consort.

Some people claim that she could at least hypothetically become Queen in her own right under the theory that she is descended from Edward VII through her grandmother Sonia Keppel: Sonia's mother, Alice Keppel nee Edmonstone, was reputedly a mistress of Edward VII, and it's possible that Sonia was his illegitimate daughter. However, Sonia's descendants have always denied this, George Keppel, Alice's husband, claimed Sonia as his own daughter, and Edward certainly never attempted to claim that he was Sonia's father.

Sonia's older sister Violet apparently made some pretensions to be of royal blood herself, though this is almost certainly not true; there's no evidence that Alice even met Edward until several years after Violet was born.

Even if the above were true: Sonia and her descendants would still be ineligible for the throne in their own right. UK law bars children born outside wedlock from the line of succession, even if their parents later marry, which Edward and Alice never did in any case.
Upon the succession of her husband to the throne, she will legally become Queen by way of being married to the King. However, it has been announced that she will be known as "Her Royal Highness The Princess Consort" rather than Queen. This preference in style, however, does not change the fact that she will still legally be Queen, unless there is an intervening Act of Parliament specifically excluding her from that title.

As wife of The Prince of Wales, Camilla Parker-Bowles now officially holds the title "Her Royal Highness The Princess of Wales," however she chooses to be known in association with her husband's lesser titles as The Duchess of Cornwall (The Duchess of Rothesay in Scotland) because the title Princess of Wales is so closely associated with Diana, Princess of Wales.

It is important to note that in the UK, the wife of the King automatically receives the title of "Queen Consort", and in the case of husbands of the Queen would normally take the title of "King Consort", but with Prince Philip he took the title "Duke of Edinburgh" over "King Consort" (he was already a prince before his marriage) after the suggestion of parliament at the time. Queen Elizabeth's father was King George VI and his wife Queen Consort Elizabeth (and later The Queen Mother).

Other responses from the community:
  • It has been said that the marriage between Camilla and Charles was not morganatic, which means she was not given monarchy powers when she married which could lead to her not being queen. Usually the heir to the throne's wife (like Princess Diana) become the next female in command, yet Camilla is below Charles's two sisters and the two young princesses.

  • It is said she will not be legally queen; however she could choose to be called Queen (consort).

    It often reminds me of the Tudor times when Anne Boleyn took the throne after the divorce between Henry and Catherine: Anne was queen in name but not to the English people.

  • Since Charles married a divorced woman, he cannot take the throne under current law. Wait and see if they change this law.