In the United Kingdom, the Queen does not have the power to choose her successor. The line of succession to the British throne is determined by established rules of hereditary succession and laws such as the Succession to the Crown Act 2013.
The order of succession follows the principle of primogeniture, which means that the eldest child of the monarch, regardless of gender, is first in line to succeed. This means that Prince Charles, as the eldest son of Queen Elizabeth II, is the heir apparent and next in line to become the monarch upon the Queen's death or abdication.
The line of succession continues down the line of descendants of the monarch, with the order determined by birth order and proximity of relationship to the monarch. The succession is not determined by the Queen's personal choice or preference.
It's important to note that any changes to the line of succession or rules of succession would require legislation and agreement among the Commonwealth realms, as the monarch is the head of state of multiple countries.