Have to disagree that it’s not a one-person hairdo. It’s a simple French braid. If she had the Barbie lay across her head with the legs pulled back so it was bent at the hips, she could very easily have done it herself and then positioned the Barbie, assuming she can French braid. You’d only need a couple rows of the braid in to hold it securely, at which point standing it back up would pull the legs closer together and tighten everything up so she could finish and have it held securely.

Or if it was left loose enough at the top the Barbie could have been added after, which the green says may be the case (or that could be colored hair gel, dunno)

(Source: had Barbies and can French braid my own hair)