Dawn Madsen and Frank Gulenchyn were supposed to be enjoying their tranquil retirement years together, a hard-earned reprieve after decades of hard work — instead, just one year in, their lives were cruelly cut short in one of the deadliest mass shootings in Canadian history.

Madsen and Gulenchyn, husband and wife, were killed during a 12-hour rampage that began late Saturday in the small close-knit community of Portapique, N.S. that claimed at least 20 victims. Investigators are still working to determine the full extent of the carnage, working to scour some 16 crime scenes left in the shooter's wake.

Madsen spent just over two decades working at the Hillsdale Terraces long-term care home in Oshawa, Ont. until her retirement in 2019, her former boss told CBC News.

The residents there held a special place in Madsen's heart, Spatzie Dublin said.

Staff at the Hilldale Terrace long-term care home threw a retirement party for Dawn Madsen less than a year ago. (Hillsdale Terrace) "She showed that kindness and respect for them ... When she came into the building, her residents were her family. And she treated them exactly like they were her family and her best friends," said Dublin. "She was like a beam of sunshine."

Madsen worked in the home's food-service department. She and her husband, Gulenchyn, had dreamed of retiring in Nova Scotia and spent years saving up for the home they wanted there.

During Madsen's last year at the home, said Dublin, the couple were apart, with Gulenchyn working to fix up the place they hoped to finally enjoy when Madsen retired.

"She worked so hard to be able to have the home that they wanted for their retirement. And now that they're together… this would happen," Dublin said.

WATCH | Dawn Madsen's former boss remembers her as "a beam of sunshine":

Dawn Madsen worked at Hillsdale Terraces long-term care home in Oshawa for more than 20 years and her former boss remembers her as a "beam of sunshine." Madsen and her husband Frank Gulenchyn were killed in the Nova Scotia mass shooting over the weekend. 0:31

Madsen was more than an employee to Dublin. She was a friend, a "sounding board," honest and contentious — the sort of person Dublin wished she could clone.

When the residents and staff learned of her death, their reaction was one of shock.

"We're trying to come to terms with what happened, not understanding why it happened and we probably never will.

"I'm distraught that something like this could happen to her and Frank," she said.

Dublin's hope now is that the couple's family knows "we're here to support them, they know that they have a shoulder to cry… we're here to support them — just like she would be here for us."

The government of Durham Region also expressed its condolences in a news release Tuesday.

"Our hearts go out to their family and all families affected by this senseless tragedy," said John Henry, chair and CEO for the regional municipality of Durham.

WATCH | Tributes to the heroes and victims killed in Nova Scotia rampage:

People across the country are expressing their sorrow over one of the deadliest mass killings in Canadian history and honouring some of those who acted bravely to protect others. 3:56

Durham will lower flags at its regional headquarters to half mast "until further notice" to honour the victims.

We can never understand these senseless acts of violence. But, we hope these communities can find comfort and support in the nation that stands behind them."

Other victims of the shooting include a veteran RCMP officer, an elementary school teacher, health-care workers and a family of three.