Shirley Warrington, 85, has not been seen since July 10 when it is thought she left her car and went for a walk near Ferrymead Heritage Park - between 8.30pm and 10.30pm
Warrington gets confused but has not been diagnosed with dementia.
But her granddaughter and one of the organisers of the Search for Shirley Facebook page, Aleisha Hofman, said there was a chance her nana could have gone further than originally expected.
She said every inch of the Ferrymead, Heathcote, and Horotane Valley Rd areas have been combed by police and the public, and she is unlikely to be there.
"Shirley and her husband Wally first went out to the Rolleston area, and my nana grew up near there in Weedons so there's always the option she asked for a ride and she's out that way somewhere."
On July 10, Shirley and Wally went out for a drive to Rolleston from their home in Burwood.
At 7.30pm the Warringtons were stopped at Rolleston by police, driving slowly on State Highway 1 towards Christchurch with their headlights on full beam, and well under the speed limit.
After a quick chat, the Warringtons were back on the road.
At 8.34pm their car was captured on CCTV camera on Ferry Rd - Wally driving and Shirley in the front passenger seat.
At 10.19pm another camera picked the car up near the Ferrymead Bridge without her.
Temperatures in Canterbury have since plunged to well below zero, -5C at one point, and Shirley was only in light clothing.
Police searched for nearly three days before confirming last week the physical search for the 85-year-old would be suspended.
That decision was explained to Warrington's family in full before police announced it to the public. They understood that everything that could have been done to that point, had been. Suspended does not mean called off, it means the full-scale search has stopped.
Hofman said the whole situation has taken a big toll on their family.
"It was quite an overwhelming feeling to think, it's basically on our family and the community to find her now but I'm grateful for everyone who's taking the time to go out and search different areas.
She said the whole family is missing Shirley and they just want her home and they know unfortunately it's unlikely going to be the best-case scenario but they want closure.
• Anyone with information that may help locate Shirley is asked to call 111 and quote file number 210711/8724
