She began her breeding program with a small number of mares whom she bred to her national champion stallion, Bay Abi.

She then acquired three mares from Arabian farms in Poland at a time when that nation was still behind the Iron Curtain and importation of horses to the United States was very difficult.

For her accomplishments, Varian received recognition from the United States Equestrian Federation, as well as several awards from various organizations within the Arabian horse industry.

For her contributions as breeder and as a horse trainer in the vaquero tradition, she was inducted into the National Cowgirl Museum and Hall of Fame in 2003.

After she was diagnosed with ovarian cancer in 2013, she sought to place the 230-acre Varian Ranch into a conservation easement to protect the land from development, and in 2015 announced that the California Rangeland Trust would partner with her to purchase the development rights and to allow her long-time ranch manager, Angela Alvarez, to operate the horse breeding program after Varian.

[7] Varian matured to be 6 feet (1.8 m) tall, and has stated that while she "struggled" with her height as a young person, she found comfort in riding horses: "all my troubles went away.

[4][6][9][14] The ranch was self-supporting from 1963 on, with the short-term assistance of loans from Sheila's aunt, Dorothy Varian, which were promptly repaid.

[15] Varian preferred the Arabian breed because "their instinctual interest in and appreciation for people runs deep in their genes.

[20] [18] In 1959, Varian and her mother Wenonah purchased a two-year-old bay stallion named Bay-Abi (Errabi × Angyl).

[23][24] Even though he was not bred to any mares until after he was fully trained, and thus his first foals did not appear in the show ring until he was 7,[25] he sired 275 registered Arabians, including 65 champions and 24 national winners.

[35][36] At the time, the Arabian industry had little interest in western disciplines, so Varian competed with her horses in English riding classes.

"[38] He sired 441 foals including three sons considered his finest:[39] his own successor at Varian Arabians, Huckleberry Bey (whose dam was Taffona, a daughter of Raffon); U.S. Reserve National Champion Bey Shah (out of Star of Ofir, who was by Bask); and Barbary (out of Balalinka (Bask x Bachantka)), who won a total of seven national titles in halter and park horse competition.

[40] Barbary was purchased from Varian as a yearling by film producer and Arabian owner Mike Nichols.

In 2002, requiring an outcross stallion not closely related to her own horses, she purchased the Brazilian-foaled Jullyen El Jamaal, who has bloodlines not previously incorporated into the Varian program, as well as a line tracing back to Bay el Bey via Bey Shah.

In her teens, she was mentored in horsemanship by Morgan horse breeder and cattle rancher Mary "Sid" Spencer.

[56][57] The Spencer property, called Forsyth Ranch, was near Arroyo Grande on land that is now under Lopez Lake.

[59][56][57] Spencer also did all of her own ranch work including shoeing, gelding, horse training, baling hay, and truck repairs.

He introduced her to his "soft approach" of working with horses, and his methods were an additional influence on Varian's training philosophy.

[9] The spade is an elaborate, complex bit that can only be properly used on a highly trained horse handled by a skilled rider.

[62] Its emphasis has always been on producing a finely tuned working horse and partner, emphasizing quality rather than on how quickly the goal is reached.

As the horse gains skill with a rider, it moves to lighter bosals, and next into a transitional period in its training; carrying a bridle with a type of curb bit called a "half breed" which is a modified spade bit worn in conjunction with a light bosal.

[3] She considered the breed to be inherently gentle,[76] and pointed out that any horse can become "hot" if they are kept in a stall 24 hours a day, fed a lot of grain, and never ridden.

[77] Varian explained the nature of Arabian horses by analogy, comparing them to precocious children who show their ability with delight, but cannot be bullied or pushed around.

[16] The Varian Arabian Ranch has been ranked multiple times as one of the leading Arabian breeders of winning horses by the United States Equestrian Federation (USEF), which since 2004[a] has ranked breeders based on points earned by horses shown in sanctioned USEF competitions.

[3] Other inductees that year included western artist Glenna Goodacre; musician, artist, cowboy poet and pickup rider Ann Secrest Hanson; and classic cowgirl trick rider and barrel racer Velda Tindall Smith (1908–1990).

[84] In November 2015, Varian announced that she would be working with the California Rangeland Trust to place her ranch into a conservation easement to protect it from development.

[96] She had begun the project with the intent that her longtime ranch manager, Angela Alvarez, would operate the horse breeding program after Varian was no longer able to do so, and then once Alvarez was no longer able to run the ranch, the property would be gifted to the Trust to be sold, the conservation easement running with the land, and attempts made to find a buyer that would also be interested in maintaining the Arabian horse breeding program.