That is according to coroner Olivia McTaggart, who said a combination of several circumstances contributed to the death of Queenstown woman Susan Ann Deuchar, 72, in the Tullah area between December 10 and December 15, 2018.

Ms McTaggart found Mrs Deuchar died from environmental heat and cold exposure with dehydration.

Following her investigation of the death, Ms McTaggart said Mrs Deuchar had an extensive medical history and was treated with chemotherapy in 2018 for multiple myeloma (blood cancer).

In her record of investigation, Ms McTaggart said Mrs Deuchar had limited mobility and used a cane for balance and support while walking.

The coroner said Mrs Deuchar on December 10 told her nephew, Carl Collins, she was going to Ulverstone for a doctor's appointment and would be back at Queenstown in a few days.

Ms McTaggart found Mrs Deuchar drove towards Ulverstone and, some time between 1.20pm and 5.48pm, she was driving north on the Anthony Rd, in the Tullah area.

At a curve about 4.8 kilometres south of the Murchison Hwy intersection, Mrs Deuchar's car continued in a straight line, crossed onto the wrong side of the road at a gentle speed and went down an embankment.

"The car stopped approximately 15 metres down the embankment and was not visible to passing motorists," Ms McTaggart said.

She said Mrs Deuchar suffered minor injuries.

Mrs Deuchar put the car in park, used the handbrake and started climbing the embankment.

"However, approximately three metres from the roadway, Mrs Deuchar either fell or laid down and was unable to get back up due to her pre-existing mobility issues," Ms McTaggart said.

"The evidence indicates that Mrs Deuchar made two separate calls to emergency services at 5.48pm and 5.49pm, but neither call connected as there was no mobile telephone reception in the area of the crash."

A friend reported Mrs Deuchar missing on December 12.

A search followed and police requested information from the public.

Dashcam footage from a motorist showing Mrs Deuchar's vehicle led to a rescue helicopter being deployed on December 15, and Mrs Deuchar's vehicle and body were seen.

Ms McTaggart said toxicological evidence indicated Mrs Deuchar did not have alcohol or illicit drugs in her system, only her prescription medications.

The coroner said it was most likely she either fell asleep while driving, became dizzy or had a lapse in concentration.

"It is likely that in the hours after her crash, she attempted to negotiate the 15 metre embankment to reach the road, using her walking stick," Ms McTaggart said.

"She then succumbed to hypothermia and dehydration, with the temperature overnight dropping to about eight degrees Celsius."

Ms McTaggart said it seemed Mrs Deuchar likely died on December 10, noting there were no further attempts to call emergency services from her phone.

West Coast Mayor Phil Vickers described the area where Mrs Deuchar died as a mobile black spot.

"Because of our terrain and mobile tower technology, I don't think it's really possible to cover every single kilometre of road around our district," he said.

"It'd be nice ...

"If it was a satellite system, we could have it.

"The towers are line of sight."

Cr Vickers said Telstra and Optus had reacted well to community concerns about providing coverage in the populated areas.