If a ten-year old girl is able to get pregnant, but her body (and bone structure) is not ready yet, doesn't that seem a bit of a problem, evolutionarily speaking?
Without a c-section, she surely would have died; her pelvis is not wide enough to allow the passage of a baby. Without modern medicine, therefore, mutations that allow girls as young as ten to ovulate would therefore eventually lead to death, so the genes involved in the mutation would not get passed on to the next generation. But modern medicine allowed her to live, and her descendants may have to deal with a similar problem.
Yes, modern medicine allows countless millions to live in spite of genetic flaws. But without modern medicine, we would surely see a massive die-off of people who have been artificially kept alive by science. Nature has a way to weed out disadvantageous mutations.