Marion Fleming – who became known as Mimi Swift – was born in an Edinburgh air raid shelter in December 1940, and spent her early life in a series of Scottish children's homes.
She was discovered by Rogers and Evans during a visit to a home in Edinburgh in 1954, after she charmed the Hollywood couple by singing a song for them.
Marion was invited to visit the couple's ranch in California on holiday and was later adopted into their large family.
The cause of her death, on Monday, was a brain aneurysm according to relatives.Her nephew Dustin Rogers posted on social media: "Today I received news that my aunt Mimi Swift passed away after a short and sudden illness (not Covid). Mimi was the sweetest soul and I just loved and will cherish our time together."
Broadcaster Stephen Jardine, 58, who interviewed Swift for a BBC Scotland programme, "Roy Rogers Kid", in 2019, and described her as “a really lovely lady”.
Others posted to her sister Dodie Rogers, sharing prayers.
Swift was born in Craigmillar, during the Second World War and from the age of two she lived in different children's homes.
She was 13 years old when Rogers and Evans visited Dunforth, a Church of Scotland children's home, where she sang a song for them. Rogers and Evans won legal custody the following year.
Swift returned to Scotland two years ago with her own three children, and recalled her time at Dunforth, Newhaven, fondly, despite its strict regime. Her duties included lighting the coal fire and preparing the house of police chief Willie Merrilees, a patron of the children's home who raised funds for them to have outings.
It was Merrilees who brought the famous "singing cowboy" Rogers and "Queen of the West" Evans to the home in 1954 while they toured the UK with their wild west show.
Roy Rogers was one of the biggest Western stars in America at the time and, along with his third wife Evans, was adored by a generation of children who watched their movies and their popular US TV show. In every city, children lined the streets for a glimpse of Rogers' trusty horse Trigger.
In Edinburgh, Rogers and Evans stayed at the Caledonian Hotel where they famously dressed in white cowboy suits and matching Stetsons and led golden palomino Trigger up the grand staircase.
The couple also visited children in local orphanages and hospitals, and performed numbers from their show. In return, young Marion sang the 19th century song "Won't You Buy My Pretty Flowers?" for the stars.
When she returned to Scotland in 2019, Swift said: "What are the chances that they would want me to be part of that family? Part of me thought 'it is not going to happen'. I was not a cute little five or six year old, I was 13. I figured it wasn't going to happen.
"When we were in the house we were just a family, they weren't Roy Rogers and Dale Evans, they were mum and dad."
Roy Rogers died aged 86 in 1998 and Dale Evans died aged 88 in 2001.