Valerie Strong could see out the window of her room at Darlinghurst's Sacred Heart hospice on her dying days – and on her happy days. She could see the National Art School's sandstone walls from there.

"She was overjoyed to be able to do that," Louise Olsen, a painter, sculptor, and designer, said of her mother. "She used to do little drawings of the place from her bed," says the narrator.

Valerie met her future husband, painter John Olsen, at the National Art School (formerly the East Sydney technical college), which was based in the historic district of the old Darlinghurst jail, in 1961. John Olsen is today regarded one of Australia's best living painters.

Louise's brother, Sydney gallerist Tim Olsen, recalls, "My father was a teacher there, and my mother was one of his students." “These days, you'd be imprisoned for that. They were also both married to other individuals at the time. They were, nevertheless, soulmates from the beginning. Dad was smitten by her femininity, integrity, and dignity."

Louise and Tim are showing me around the first exhibition of their mother's art. It includes 67 prints, sketches, and watercolour paintings, the majority of which are from Louise and Tim's personal collections. The majority are on display for the first time.

Louise looks around the room and adds, "It's actually quite emotional." “I really miss her.”

In 2011, Strong passed away.

Louise says, "She left us an incredible body of work that she created quietly." "She was unconcerned about getting recognized for her work. She acted as though she didn't have an ego.”

Valerie Strong was born in Sydney and spent her childhood with her family in New Guinea. When the Second World War broke out, they returned to Australia. She worked as a millinery designer after graduating from high school, finally earning enough money to attend East Sydney Tech.

The first paintings you see in the show are from those early years, such as Afternoon Yarramalong, a bush scene made in 1963.

Tim explains, "It's about her feelings about the bush." "It would have started out in the field but ended up in the studio, so it's all about memory." Mum was a firm believer in the power of memory."

At this moment, Strong was under the supervision of John Passmore, he says. "In his teaching, he was almost like a Zen Buddhist, very much against the vulgarity of the art world." That was something he instilled in my mother. He sought to convey the concept of selflessness, that nothing should stand in the way of the truth.

"Passmore was the polar opposite of my father, who enjoys conquering the terrain in his art and exudes swagger and boldness. My mother, on the other hand, was content to be at one with nature."

Strong was a restless genius who was continually experimenting with new forms, despite his self-effacing demeanor. A trio of miniature paintings, Yellow Room (1970), Dam at Dunmoochin (1970), and The Red Leaf (1970), show one such transition in style (1971).

The Olsens resided in Dunmoochin, an artists' colony north-east of Melbourne formed by a group of artists including Clifton Pugh, during that time. It is still in use today.

Louise explains, "We lived in a mud brick house with no electricity or hot water overlooking a dam." It's captured in "Dam at Dunmoochin." Mum worked for a long time to perfect that murky palette."

Tim describes it as "a pretty outrageous time." "Louise was six years old, and I was eight." It was all very 1970s – highly tumultuous, with a lot of nudity and philandering."

Strong opted out of the competition. "She'd be getting the tea together in the background," Louise adds. "She was content to float along with it, but she kept to herself."

Strong's interest in blooming plants began in the mid-1970s. "She'd go out into the woods with a magnifying glass," Louise recalls. "She was staring at nature intently. Although several of these paintings seem to be abstractions, they are not. Take a look in nature and you'll see these shapes."

Many of Strong's paintings have a delicate quality to them. Tim describes her as a “slow painter.” "She'd work on things for years, then put them away and bring them back out." "Knowing when to stop can be as difficult as knowing when to start," she used to remark.

Tim shows to Strong's painted irises. He explains, "They were grown from bulbs she smuggled in from Kyoto." "It's too late now to be arrested."

Louise pulls me in a little closer. "Take a look at her orchids local to her area. She would work on this tone for six months. She worked with a special watercolour paper and a very delicate brush, layering color one on top of the other. She was enthralled by the procedure and the attention to detail.”

Although figurative works make up a minor portion of this collection, Strong was an ardent portraitist and life drawer. Margaret Olley with Pomegranates, painted in 1985, is one of the portraits on display.

“I'll never forget Margaret telling me, 'Your mother... she's a good painter, but she takes a long time!'” Tim laughs. “Margaret wasn't known for her patience; she preferred to get right to the point.”

According to Louise, the portrait took almost two years to finish. "Mum liked to sit in her chair and daydream about it." They were fantastic pals. Margaret's candor was admired by Mum. There was no equivocation."

The contrast between John Olsen's work's colorful excess and Strong's concentrated humility is startling. It's difficult to see them living together.

Tim describes his parenting as "yin and yang." "Dad was the rock star, but Mum was the one who gave us our foundation and self-esteem."

Did she ever feel like she was being overshadowed? Tim isn't convinced.

"It was her preference." She had no desire to be in the spotlight. There was a moment for her to speak out and a time for her to remain silent. Every day, I'm continuously learning that lesson."

Louise remembers her mother being "very hands-on."

"She believed it was critical that Dad continue to paint in the studio while she looked after us." She painted in the early mornings and when we were in kindergarten. She managed to find the time. Mum had no desire for celebrity. She was overjoyed that Dad had discovered his and that she could make her own art for no other reason than she like it."

Thanks to Elissa Blake at The Guardian whose reporting provided the original basis for this story.