Prince Charles

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 Answers.com 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.

He doesn't actually earn anything "as prince". His earnings come from investments and from him also being a duke, specifically the Duke of Cornwall (this title vests automatically in the eldest son of the reigning monarch; if the monarch has no sons, the income from the estate goes to the crown instead). In 2010, Charles received about 17 million pounds in income from the duchy, of which he spent about half on public and charitable works.

He is not legally required to pay income taxes on his revenues from the duchy, though he has done so voluntarily since 1969 (in 2010, for example, he paid 40% income tax, which is the same rate anyone else with that income would be required to pay).

You didn't ask, but at least some of the other princes in the Royal Family do have earnings "as princes" ... it's complicated, but boils down to Parliament paying them an annuity for performing various official duties, and then the Queen paying parliament back out of her personal funds. In other words, they effectively get an "allowance" from the Queen.

The Queen herself gets a little under 8 million pounds a year from something called the Civil List, in exchange for turning over revenues from the Crown Estate. 8 million seems like a lot, but it's actually a fantastic deal for the British government, since revenues from the Crown Estate were over 210 million pounds in 2010.

The truth is that only Prince Harry and his immediate family will probably ever know for sure his true paternity. What is certain is that, until her death, Princess Diana vehemently stated that Prince Harry was the son of Prince Charles.

Opinions from Answers.com contributors on both sides of the issue:

• It's Prince Charles. In the 1990s a DNA test was done on both Prince William and Prince Harry, and both were found to be Charles's sons.

  Harry's red hair is a Spencer trait, which comes from his mother's side of the family. And if you look at Harry's face, he has some of Charles's features, notably his eyes, which are too small for him to be Hewitt's son with Diana (both of whom have larger eyes).

  Diana's affair with Hewitt didn't even begin until after Harry was born. Both stated this and yet Charles's camp lets these nasty rumors continue in order to promote himself and his current wife, Camilla, Duchess of Cornwall.

• No one knows. To say a DNA test was done on both Harry and William in the 1990s is totally false! How did such a spurious statment get on here? The fact is that no DNA test has ever been done on either William or Harry! And, there has never been any question over who is the father of William - no one disputes, or ever has disputed, that it is Charles. But, see below regarding Henry (nicknamed Harry):

  "Even more shocking is the possibility that Harry, 22, third in line to the throne, might not be a Windsor. If true, and there is no scientific proof, it would be the ultimate payback by Diana against her ex-husband, Prince Charles."

  Christopher Andersen's book, his third about Diana, is an attempt to "defend her honor" against 10 years of calumny since she died. "It's about her legacy and the new generation," he says. "She has been portrayed as scheming and neurotic, and it's patently unfair. For all her faults, and she had plenty, she was a pretty gutsy young woman."

  But perhaps reckless. Diana and Hewitt separately denied he was Harry's father, saying they hadn't met until two years after Harry was born in 1984. But Andersen names witnesses, such as British public relations guru Max Clifford, who say that Diana and Hewitt met as early as 1981 and that they were lovers by January 1984, nine months before Harry's birth.

  "It's not just the physical resemblance - and I can pick out dozens of photos that show this - it's the peculiar expressions, the walk, the mannerisms" the two share, Andersen says.

The Royal Family has, understandably, refused to discuss publicly the cost they incurred for the wedding, which were met jointly with Catherine's parents, Mr and Mrs Michael Middleton, and covered all the 'normal' wedding costs that any family would incur: the hire of the church, the wedding cars, the flowers, the dresses and the reception. They did of course have the benefit of owning the main reception venue, Buckingham Palace and the fleet of carriages with horses.

Estimates from the Metropolitan Police put security costs at £7 million. The department of Media, Culture and Sport spent a further £4m on decorating the route to and from Westminster Abbey, although final figures show that this expense was more than offset by the distribution rights levied by that same Department on UK and overseas TV companies. It is believed that in the year 2011, wedding-related tourism generated £4 billion.

Furthermore, £107m was estimated to have been spent by visitors to London that weekend, and a further £400m by people across the country on parties, whereas in the coming year (2012), the boost to tourism generated by the aftermath of the wedding and, more especially, the Queen's Diamond Jubilee is expected to be worth a further £6 billion. (UK government department cumulative estimates). Clearly, pageantry, which Britain does so well, generates revenue that far exceeds the costs involved.