Her passenger had asked her to stop so they could look at a well-known kayaking rapid.
Their van collided with a ute of which Saunders was the sole occupant, and his vehicle crashed about 100 metres down a steep bank, ending partly submerged in the river.
Two members of the public climbed down the rock face and found him trapped and unconscious.
The pair kept his head above the water until emergency services arrived, but he died at the scene about 90 minutes later.
Riviere, a French national who has been living in New Zealand on a working visa for two years, suffered facial and other injuries from which she is still recovering.
Saunders and his wife, Holly, who have four children aged seven to 16, own Central Wilding Tree Control Ltd.
Several members of the family and friends read victim impact statements at the hearing.
His wife, Holly, said her family spent an ''unbearable'' Christmas Day with her husband in a coffin at their home.
She felt ''dead inside'', and had been relying on her mother to look after her and her children.
Her husband was ''a good man, a man of honour, integrity and strength''.
''Cecile, you took my soulmate from me . . . you killed me also.''
Counsel Tim McKenzie said the defendant had been careless in failing to check the road ahead was clear, but there were no exacerbating features such as speeding, alcohol or use of a phone.
The defendant had been prepared to meet Saunders' family under the restorative justice process, but the family had chosen not to participate.
Judge Brandts-Giesen said careless driving mistakes did not usually lead to such tragic consequences.
''There was nothing to suggest that until milliseconds before this accident, she was driving dangerously or carelessly.''
In sentencing the defendant, he took into account her remorse, clean record and willingness to engage in restorative justice.
In addition to home detention, she is disqualified from driving for 13 months, must pay reparation of $12,500 to the Saunders family, and complete a driving improvement course.
