'Childlike innocence' of JFK's eldest sister Rosemary is revealed in unseen letters she wrote aged 20, three years before being forced to undergo a lobotomyRosemary Kennedy, John F. Kennedy's oldest sister, would have celebrated her 100th birthday today New unseen letters reveal how she was a vivacious young woman prior to being left with a severe mental disability after having a lobotomy aged 23 The letters were written to Dorothy Smyth who looked after Rosemary while in Ireland and England in 1938 Smyth died in the 1960s, but her family kept the letters according to her nephew, Michael Fisher who described them as holding a 'childlike innocence'[/size]By REGINA F. GRAHAM FOR DAILYMAIL.COM PUBLISHED: 17:37 EDT, 13 September 2018 | UPDATED: 12:50 EDT, 14 September 2018