I was a runner for nearly ten years, beginning when I was 58. Nothing extreme, just 5 and 10k races, with practice runs a few times a week. I do not have osteoporosis, but I lost an inch in height because of the pounding on my spine. I now walk a 5k a few times a week. My back, hips, tendons and muscles no longer ache or hurt as they did while I was running.
Depends on your build and how one runs. Running for top speed is hard on the body. Running at slower speeds - how slow is individual - is not hard on the body.
She’s been doing extreme runs for years so she is obviously well built for running. If she was abusing her body by doing this, she would NOT have been able to do daily marathons.
Could I do it? Nope. Not even close. A typical good distance runner weights in pounds about twice their height in inches. That isn’t me. You need to genetically have a large bone cross section for your weight and near perfect alignment.
Me? At Medicare age, 15 miles a WEEK is plenty. Down from 25 miles a week when I was younger. A marathon would kill me. But I’ve never been an elite runner. Wasn’t born for it. But I’ve been jogging for 50+ years and haven’t lost height or damaged my knees.