Well first of all, most of those girls probably started some form of that position from an early age. I’ve heard of parents not allowing their children to practice ballet or the such like due to potentially causing mobility problems down the line. It’s a double edged sword… start early and you can achieve these positions, but you may learn say a collapsed ankle position, or lack of motor control due to having too much ROM.

If your friend wants to hit that position now, she just needs to keep working at it. A good place to start is simply being in that position more throughout the day. If I want to work on the bottom of my squat, I sit in the bottom position of the squat multiple times a day. After that, lots of smashing, banded distractions, voodoo flossing anything and everything in the area. Best of luck!