An American student who survived a horrific car crash near Turangi that left three of her friends dead has flown home, but she's determined to return.

Meg Theriault, 21, suffered critical injuries in the May 12 crash and spent two weeks in a coma in Waikato Hospital.

She flew out of Hamilton on a medi-flight bound for Boston, Massachusetts on Wednesday.

In a statement released by Waikato District Health Board, Ms Theriault's parents Todd and Deb said they've been overwhelmed by the support they've received.

Ms Theriault's mother said her daughter will return to New Zealand once she's finished her studies at Boston University.

"She will thank everyone in person and she will do that Tongariro Crossing. She's a determined girl and as a family we'll be here to support her."

Earlier on Wednesday, the 20-year-old driver of the minivan, Stephen Houseman, pleaded guilty at Auckland District Court to three counts of reckless driving causing death and four counts of careless driving causing injury.

Houseman was convicted and discharged, except for being disqualified from driving for six months, and ordered to pay court costs.

The group of Boston University students, who were on a study programme in Auckland, were on their way to walk the Tongariro Alpine Crossing when Houseman lost control of the minivan when it hit gravel.

Four students, who weren't wearing seatbelts despite being asked by Houseman to put them on, were thrown from the vehicle.

Daniela Lekhno, 20, Roch Jauberty and Mr Brashears, both 21, died at the scene.

Judge Brooke Gibson said the consequences of Houseman's actions far outweighed his level of carelessness, which he described at the lower end of the scale.

Ms Theriault's parents Deb and Todd have since met with Houseman's mother and father.

"This was an accident after all - our kids were pursuing their dream. Nobody was intentionally doing anything that would harm anyone," they said in a combined statement.