They sold everything they owned, wrote letters to their creditors and gave up their apartment in Sierra Vista, Ariz.
Then they drove north to Alberta.
Court heard Tuesday that the women decided to end their lives in a tent, pitched in a secluded mountain area near Rock Lake, about 350 kilometres west of Edmonton.
On May 8, they swallowed some sleeping pills and injected themselves — and their two dogs — with insulin, according to a prepared statement put into the record by the Crown. Next, they opened a propane tank inside the tent and went to sleep.
Shirley Vann, who was in her 70s, never woke again. The dogs also died.
But 53-year-old McNall survived, despite at least three more suicide attempts over the next two days.
Following a psychiatric assessment, McNall pleaded guilty in Stony Plain court to a charge of aiding a suicide. She is to be sentenced Jan. 7.
Crown prosecutor Robert Marr said he may ask McNall receive time served for the eight months she has spent in pretrial custody.
He believes the assisted suicide case is the first in the province. There have only been a handful of other cases in Canada, and those offenders got suspended sentences, he said.
Whatever the judge decides, McNall will be deported back to the U.S., said Marr. A doctor has also recommended she be transferred to a hospital there to receive treatment for depression.
Court heard details of how resolved McNall was to kill herself alongside her mother.
McNall woke some time after she and her mother had first closed their eyes. She discovered the propane tank was empty and opened a second container, but didn't succumb to the gas.
Unable to rouse her mother, court heard McNall drove her Jeep Wrangler into the nearby town of Hinton and bought another tank. But, back at the campsite, she discovered she was unable to open it.
"As it was now too late to return to town and it was cold outside, she dragged Shirley, who was still breathing but unconscious, into the vehicle to stay warm for the night," Marr said in a prepared statement to the court.
A determined McNall travelled back to Hinton the next day and bought a hose to release the gas from the bottle. She took more pills and drifted off to sleep.
When she woke up again, she discovered her mother was dead.
"McNall made another trip back to Hinton where she withdrew money from an ATM Machine. She purchased another bottle of propane and some food," said Marr. "She once again opened the propane bottle and took more painkillers."
About 2 a.m. on May 10, when she woke to discover she had failed again, McNall drove with her mother's body still in the Jeep to the Hinton hospital.
Marr said staff pronounced Vann dead and two propane tanks were discovered inside the vehicle, still releasing gas.
McNall received medical care and was charged by RCMP four days later.
A medical examiner determined her mother died from insulin and propane toxicity.
Vann previously had colon cancer and suffered other health issues as a result of surgery. Marr said an autopsy found no active cancer in the woman's body.
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