Life expectancy at birth is different from life expectancy at given age. Each year you manage to survive after birth increases your current life expectancy, because you already managed to avoid all causes of death up to that point.
(And assessing the average woman of her age now is not likely to change it that much; AFAIK life expectancy in the USA is actually falling slightly across all age groups)
The issue is, she's not an average woman, at least in terms of physical fitness.