But at what cost?
Two of her brothers are now voicing concerns for her well-being and speaking out about her ability to handle the pressure of global stardom.
"The traveling and the whole [fame] thing is exhausting. She still has her anxieties and her loneliness," her brother Gerry tells PEOPLE in the latest cover story.
Her other brother, John, is even more blunt: "She needs 24-hour care. She needs to be looked after."
To ease her fears following a break-in at her home last month, Boyle, 48 – who lived with her mother until she died in 2007 – makes late-night calls to her family and friends, and her management installed 24-hour security outside her home.
And when that's not comforting enough, "She knows she can come up to me anytime," says her longtime friend Lorraine Campbell. "If she's upset, she'll stay the night. Security would bring her up to my house. I take her home in the morning. Susan stayed with me a week ago. Nighttime is a lonely time for her."
For more on Boyle's struggles, pick up the latest issue of PEOPLE, on newsstands Friday