AP Style holds that you should capitalize “queen” only when used before the name of royalty. For example,
- Today, Queen Elizabeth II knighted Elton John.
Continue in second references that use the queen’s given name. For example,
- Today, Queen Elizabeth will make an address.
Lowercase “queen” when it stands alone in sentences. For example,
- Today, the queen is expected to make an announcement.
Capitalize in plural uses. For example,
- Of all royalty, Queens Elizabeth and Victoria were the most majestic.
See also AP Style Nobility, AP Style Titles.