Legally, she would be "Camilla Shand, Duchess of Cornwall" with divorce. Her style would be "Camilla, Duchess of Cornwall" as the former wife of a peer.
The Mountbatten-Windsor surname does not apply to descendants of The Queen and Prince Philip who were/are HRH.
I'm not sure about the who "were" - but I'm pretty sure that if you are right then she would be Camilla Windsor - you need not revert back to your maiden name on divorce.
just checked:
If you take these two declarations into account, Camilla would be Camilla Windsor, duchess of Cornwall.
from:
Royal Styles and Titles of Great Britain: Documents
House of Windsor (Feb 8, 1960)
At the Court at Buckingham Palace, The 8th day of February 1960.
Present, the Queen's Most Excellent Majesty in Council.
Her Majesty was this day pleased to make the following declaration:
"My Lords
Whereas on the 9th day of April 1952, I did declare in Council My Will and Pleasure that I and My children shall be styled and known as the House and Family of Windsor, and that My descendants, other than female descendants who marry and their descendants, shall bear the name of Windsor:
And whereas I have given further consideration to the position of those of My descendants who will enjoy neither the style, title or attribute of Royal Highness, nor the titluar dignity of Prince and for whom therefore a surname will be necessary:
And whereas I have concluded that the Declaration made by Me on the 9th day of April 1952, should be varied in its application to such persons:
Now therefore I declare My Will and Pleasure that, while I and My Children shall continue to be styled and known as the House and Family of Windsor, My descendants other than descendants enjoying the style, title or attribute of Royal Highness and the titular dignity of Prince or Princess and female descendants who marry and their descendants shall bear the name of Mountbatten-Windsor."
(
London Gazette, issue 41948, Feb. 8, 1960, p. 1/1003. See also the
Times Feb 9, 1960 p. 10E.)
Former Wives (1996)
Buckingham Palace
The Queen has been pleased by Letters Patent under the Great Seal of the Realm dated 21st August 1996, to declare that a former wife (other than a widow until she shall remarry) of a son of a Sovereign of these Realms, of a son of a son of a Sovereign and of the eldest living son of the eldest son of The Prince of Wales shall not be entitled to hold and enjoy the style, title or attribute of Royal Highness.
(
London Gazette, issue 54510, Aug 30, 1996, p. 1/11603.)