After the leak RTS has today confirmed it's indeed 22-year-old Sanja Vučić. They didn't however confirm the song is the rumored Shelter, penned by Ivana Peters (who may or may not have been RTS original artist choice for 2016). The song will be revealed next week. It's apparently about violance against women, thus following the direction RTS took last year with Bojana and the song is, sigh, in English.
Sanja was the lead singer of band ZAA that has toured all ex-Yogoslavia and released albums.