Shannan Watts' mother opened up about her daughter's death during an interview with 20/20, says she's still going to "fight" for her

There’s not a day that goes by that Sandra Rzucek doesn’t think about her daughter, Shannan Watts.

The grieving mother has opened up about her daughter and what life has been like since Shannan, then 15 weeks pregnant with a baby boy, and her young girls were murdered in August at their Colorado home by Chris Watts, Shannan’s husband.

“You know someone asked me a question one day, ‘Sandy how are you standing?’ Well, I have a fight to fight. That’s my daughter. I gave her life, and I’m still going to fight for her… you know?” Sandra explained to ABC News in her first-ever interview since the brutal killings in an episode of 20/20, which aired Friday night.

“Those grandchildren… they were my everything, they were my only grandchildren in the whole world,” Sandra said, fighting back tears while sitting next to her husband Frank.

Frank and Sandra described Shannan, 34, as a determined woman, who had overcome the risks of her lupus diagnosis to have children, who were her “miracles.”

“She was fun, full of life. She did so many things,” Sandra said.

“She had her hand in everything,” Sandra said. “She was amazing.”

Sandra said her daughter “never gave up” and kept a vision board — “to make sure her children had everything they ever needed,” Shanann’s father explained.

Shannan Watts and her daughters
| Credit: Shanann Watts /Facebook

“She was a good soul,” Frank told ABC.

Both he and Sandra described Shanann as confident, resolute. Before giving birth, she had dreamed of being a mother, Sandra said, and for years she battled lupus, an autoimmune disease.

When Shanann became pregnant with Bella, her oldest daughter, some of her friends grew concerned about the health risks, Sandra said.

She recalled telling Shanann, however, “God wouldn’t let it happen if it wasn’t meant to be.”

RELATED: After Killing His Pregnant Wife, Chris Watts Claimed Baby She Was Carrying Wasn’t His

“She would do anything for her children,” Frank said. “She just loved her children, and she wanted them to have everything growing up.”

Sandra and Frank also opened up about their daughter’s relationship with Chris, explaining they knew her marriage was having problems and that Sandra had advised her daughter to give her husband of nearly six years space.

“She just couldn’t understand why he was so cold,” Sandra said.

The Rzuceks also noted that Chris had been exhibiting strange behavior and appeared to be extremely distant.

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Chris and Shannan Watts
| Credit: Shanann Watts /Facebook

“Nothing that was really — that I could physically see,” Frank told ABC. “Something wasn’t there, but [it] didn’t click to nobody.”

Sandra said the estrangement seemed to have been going on for a “few weeks, maybe a month.” Chris acted “just cold as ice,” she said, not replying, not responding.

“I just said, ‘Give him space,’ you know,” Sandra recalled. “But little did we know.”

In fact, prosecutors later revealed, Chris had grown infatuated with a co-worker with whom he began an affair that summer before the murders.

Watts sentenced to life
Chris Watts
| Credit: RJ Sangosti/The Denver Post/Getty Images

Motivated by his desire for a “fresh start,” he strangled Shannan at their Frederick, Colorado, home early on Aug. 13 and smothered their daughters, 4-year-old Bella and 3-year-old Celeste. Then he hid their bodies and publicly pleaded for their safe return.

Chris was arrested soon after the murders and confessed to killing his wife — but claimed he did so only after watching her strangle Celeste in apparent retaliation for announcing he wanted to split.

When in November Chris surprisingly pleaded guilty to all of his charges, to avoid being executed, he confirmed that earlier confession was a lie. He will spend the rest of his life in prison.