Now, however, her story is also being cast as a cautionary tale after Boyle threatened to quit the show due to pressure.
"She's been in tears repeatedly," Piers Morgan, one of the show's judges, told "Inside Edition" in an interview aired in the United States on Thursday.
"And, as of yesterday, she was packing her bags."
In his blog, Morgan wrote: "Let me tell you now, there is a downside to fame. People start criticizing you, sniping at you, trying to trip you up, belittle you, harass you."
He said Boyle had learning difficulties after being deprived of oxygen at birth, and was nicknamed "Simple Susan" at school.
"I am calling today for everyone to just give her a break."
Both of Britain's main tabloid newspapers dedicated their front pages to Boyle on Friday, focusing on what they said was her erratic behavior and concerns among executives at ITV, the channel which airs the show, over her ability to cope.
Susan's brother John told the Sun: "Celebrities have professional people who insulate them from these stresses, but she hasn't had this protection. The show's producers should have been looking after her more."
ITV would be reluctant to axe Boyle from Saturday's final, with her success contributing to bumper ratings figures and advertising windfalls.
Boyle's semifinal on Sunday was watched by an average of 11.8 million viewers over 90 minutes, or 49 percent of the total television audience during the same period.
The audience rose to 13.2 million on Monday and 12.7 million on Tuesday, according to media reports, which also estimated advertising revenue from the five semifinals and final reaching nearly 20 million pounds ($32 million).
Other performers through to the final include singing act "2 Grand", comprising 76-year-old John Neill and 12-year-old Sallie Lax, and father-and-son comedy dance duo "Stavros Flatley".