Regarding female titles,and who uses them...this from wiki:
// She and her sister are the only granddaughters of the Queen to use the title of Princess of the United Kingdom of Great Britain and Northern Ireland and the style Her Royal Highness: their cousin, Lady Louise Windsor, is styled as the daughter of an earl at the request of her parents; their other female first cousin, Zara Phillips, is the Queen's granddaughter through the female line, therefore allowing her only the title and style of her father, who has none. //