When I was young, svelte, and agile I could move like this, climb up a tree in matter of seconds. It’s easy to hold your own weight when you don’t weigh that much. Looks legit. Probably something she practiced for fun and it came in handy one day.
Your post reminded me of my time at Navy Officer Candidate School. One guy in our company who was of a slight build could do pullups forever. Another guy had legs I swear were twice as long as mine. Keeping up with him on a run was so hard. Friday was sports night and the OC in charge for our company always assigned me to swimming. Not because I was capable, but because even when you finished last your company got one point.