The exact cause of her death has not been officially disclosed. However, Sisic had suffered from a congenital heart valve defect since birth and underwent seven heart surgeries throughout her life.
Despite her health struggles, she had spoken openly about her condition, saying she did not want people to feel sorry for her but instead hoped her story could give strength and courage to others facing similar challenges.
Sisic was crowned Miss Austria in 2024 and remained the titleholder until her death. Her final heart surgery took place during the winter of 2025, after which she shared her relief at having completed her seventh procedure.
Her death prompted an outpouring of tributes, with Mission Austria describing her as a remarkable young woman who would always remain part of the pageant family.