My take on it. The young girls went up to the moutnain to become free. Key elements. Taking off of the shoes and corsets. both can be seen as articles of confinement. The youngest girl ran back screaming becasue the world of the free is the world of the wild and untamed something she was not up to. I suspect the raven hair lass had the same feelings. Notice when she's leaving the school she's decked out full gentle lady's costume.

Conclusion is also based around constant brid imagery in the movie.

Questions...

Is their any signficance in raven heaired girl's hands being scratched but not the rest of her?

What book was the one teacher reading/writing? Geometrical shape of something.

Watches stopped at twelve because....My guess is that the Hanging Rock represents another place. Possibly the dreamcountry of the Australian outback.

Second guess on what happaned to the young ladies....
They turned into swans.