Guess the 1960s song lyrics #54

1960. This singer had her first hit at age 12. By 14 she had a hit with a Christmas song that still gets played every season. She got the nickname Little Miss Dynamite because she is only 4'9". She was 15 when this song hit #1. The song was not released for several months after it was recorded for fear that she was not mature enough for a song about unrequited love.