So you're probably wondering why her hair mostly still flops down when there is no "down?" shouldn't it look like an chaotic explosion? As near as I tell as a nonexpert:

Inertia. The harness keeps yanking her down from stride to stide. This gives a stronger vector towards the treadmill.

Preferential hair curvature. Maybe she recently came up and being a pony tail wearer in a gravity field, her hair strands which consists of dead skin cells, after repeated washings and gravitational stress is mostly curved in a downward direction.

The second point I'm mostly iffy on. For example what whould happen if she cut her hair down to stubble and spent a year in space. Yes, her follicles would still have their genetic shape giving her straight hair. But the gravitational stresses wouldn't be there. So, I'm guessing here, her pony tail wouldn't have that preferential curvature.

I don't know.

