Your progression makes sense and getting sub 20 as female is not easy at all, it's like a male running 17 flat or low 17.
Turtle was fast in HS, but then mostly sedentary for many years, and also injured at the end of her HS career. She still has the great speed that she has (not 62, but mid-high 60s she can probably drop these days). 6 min mile is not her current ability, but she will be able to run that again if she keeps training and improving.
I had decent speed after 6 years of being sedentary (and was not even a 6 flat miler as kid despite being physically active) but absolutely no endurance and leg strength, and 11 min miles were hard. Rock climbing gave you very good shape/fitness in general, being completely sedentary you would struggle to even run 1-2 miles and certainly not break 60 in a 10k.
When the HR/cardiovascular system becomes the limiting factor, running even 10 min miles becomes quite hard so I see no reason to doubt Turtle's PR's or current speeds. They are typical for a beginner, but what should happen is that since she already was on a high level once, she should be able to reach it again eventually if she keeps training. So the current 11 min miles will become 10 min miles soon, then 9 min miles, 8 min miles etc..