:::::::It specifically says "..her reign, which at 59 years is one of the longest for a British monarch..". That's why I suggested that we could change it to "..her reign, which at 59 years is the second-longest for a British monarch.." at the end of this week.  
 :::::::The lead is supposed to be a summary of the entire article; it won't be an adequate summary if her early life, annus horribilis and Diana's death are removed.