The crash became a story of unimaginable tragedy for NSW Police Sergeant Steven Underhill, who was called to the scene only to discover his daughters were trapped in the wreckage.

Courteney Matthews, 18, was driving a red Mazda 323 with sisters Elle, 4, and Elaina, 2, in the back seat on December 18. A third girl, aged seven, was in the front passenger seat,

Ms Matthews' car was torn in half when it was involved in a collision with a Subaru Liberty about 10 kilometres east of Casino about 1.20pm.

Elle was killed, while Elaina was flown to Lady Cilento Children's Hospital, in Brisbane, with serious injuries. The third girl was treated in hospital for shock.

The 81-year-old male driver of the Subaru was taken to Lismore Base Hospital with an injured sternum.

Ms Matthews, who had just finished year 12, was taken to Lismore Base Hospital with a cut to her arm.

On Thursday afternoon, police confirmed they had charged her with a slew of dangerous driving charges.

She is expected to appear before Casino Local Court on July 20 on charges of dangerous driving occasioning death, dangerous driving occasioning grievous bodily harm, negligent driving occasioning death, and negligent driving occasioning grievous bodily harm.

Sergeant Underhill, who was on duty for Richmond Police Local Area Command, was unaware his daughter had been involved in the crash until he arrived at the scene.

"[He] tried desperately to help but was suffering shock," witness Tazman Currie told The Courier-Mail in December.

The devastated mother of the girls, Michelle, also arrived soon after.

Hundreds of people, including Deputy Police Commissioner Catherine Burn, attended Elle's funeral at St Mary's Church in Casino in January, where her small white coffin was carried out to the song Amazing Grace.

Afterwards, her mother and Elaina released butterflies into the blue sky.