S/he is quite exceptional, I'll admit that. But if you look at the photos closely you can see that s/he has had work done around the waist:
It's visible in the other pics as well.
(Credit where credit is due: s/he could have photoshopped that out, but didn't.)
Also, Lauren Prado's arms, although thin, don't seem to have the same hyperextending elbow joints that women often have.