One witness followed the woman's car and called emergency services.
When officers arrived, Wallis drove her car over a 10-metre bank and into the Waikato River.
Four police officers went in after her and, assisted by a kayaker, brought her to shore.
She was hospitalised with moderate injuries.
A witness told the Herald he was swimming in the river when he heard a crash.
He looked up and saw the car drive over the bank.
The car flipped before plunging into the river.
The man said he ran to find Wallis had managed to pull herself out of the car.
A boatie who transported her to waiting paramedics, said she had a number of cuts to her face and hands.
"The impact of personality disorders on offending and the risk to the public in future are of great significance," said Crown prosecutor Ross Douch.
Justice John Fogarty accordingly ordered a report to address those factors as well as one to assess the suitability of home detention.
Wallis will be sentenced in October.
