1970s story of preschooler dying of CF

There was a story in I think Readers' Digest back in the '70s about a girl who died of CF at age 4 or 5. The story was written from the family's point of view. She had her parents by her side, but her older brother, who I think was in 1st or 2nd grade at the time, was sent to school on the day the parents knew his sister would die.

It was very touching, although it left you wondering "what if" - "what if the boy had been able to watch death happen."

At the time the average CF patient didn't live to see high school, now they live well past 20, so this particular child probably would have lived at least twice as long if not to adulthood.