She:
- was born in a time with no antibiotics
- lived on a farm with all of it's inherent risks
- lived through World War 1 (granted in the United States)
- survived the "Spanish Flu" (although as someone under 10 whereas hardest hit were adults)
- lived through the Depression
- started having children post World War 2 (now with antibiotics available).
I've often thought, just making it to age 10 showed that she had a strong immune system. When she started having children, she benefited from having access to antibiotics at a time when there was no drug resistance.
Looking at my parents generation (the baby boomers) and suddenly you have a generation of children where infant mortality etc goes way down (again thanks to antibiotics). In other words, children that wouldn't have survived in 1912 are now living into adulthood. We applied selection pressure to have children (and then in turn adults) with weaker immune systems. (Not saying this is a bad thing).
Because of the above, I wonder how much of the life expectancy increase has to do with a kind of winning the demographic lottery of: "When I was little, my immune system kept me alive. When I was an adult, medicine took care of what my immune system couldn't."