I'd have a good look at her because that isn't normal. She might have the condition where her muscles don't produce that much acid.
Good News
You would be surprised this is not even close to the limit of human endurance. There is for example the spartathlon run (250 km in two days) and the extended version, where people run from Athens to Sparta and back again in 4 days like the messenger of old did. That's 500 km in 4 days.
Just because it's possible, doesn't mean it's normal.
If they start selling that in pill form, I hope she gets hella royalties.
It’s not a problem. It’s adaptation. The human body is incredible, though different people will have different levels of ability so adapt to different stimuli. Thats why some people become olympians and some miss out despite training, eating, and sleeping in the same group.
Lactate buildup is acute, and not likely a factor in the ability to perform repeating ultramarathons.
Incredible achievement!
I know its superhuman