Soprano Štefica Graselli began her professional career during her studies at the Academy of Music in Ljubljana, where she completed both her undergraduate and master's degree with Professor Pia Brodnik. Upon finishing her studies, she was awarded her diploma with highest distinction (summa cum laude) and received the Academy of Music's Prešeren Student Prize in recognition of her outstanding achievements in concert and operatic performance.

She has collaborated with numerous conductors, including Igor Švara, Simon Dvoršak, Marko Vatovec, Aleksandar Spasić, Egon Mihajlović, Marko Hribernik, Simon Krečič, Jaroslav Kyzlink, Loris Voltolini, Živa Ploj Peršuh, Mojca Lavrenčič, David Švec, Roberto Gianola, Mate Bekavac, Ayrton Desimpelaere, Aleksandar Marković, Marco Guidarini, Philipp von Steinaecker, Jakob Barbo, Črt Lasbaher, and Iztok Kocen, as well as with stage directors such as Detlef Soelter, Yulia Kristophorova, Rocc, Frédérique Lombart, Diego de Brea, Matjaž Farič, Aleksandar Popovski, Jiří Nekvasil, Frank Van Laecke, Krešimir Dolenčić, Marin Blažević, Emanuele Gamba, Eva Hribernik, Luis Ernesto Doñas, and Alessio Pizzech.

Štefica Graselli has appeared in numerous concerts, achieving great acclaim for her performance in Monteverdi's Vespers for the Blessed Virgin (Vespro della Beata Vergine) in Ljubljana and Berlin, as well as in Charpentier's motet Te Deum in Ljubljana. During the 2014/2015 season, she performed Pergolesi's Stabat Mater together with the Academy of Music Baroque Orchestra and the ballet dancers of the Slovene National Theatre Maribor, in choreography by Edward Clug. Under the auspices of Glasbena mladina Slovenije (Musical Youth of Slovenia), she also gave solo recitals at such venues as Križanke and Slovenian Philharmonic.  

Notably, she performed at the commemorative concert of the Glasbena Matica Music Society, dedicated to the composer Samo Vremšak, where she presented his song cycle Eight Songs from Gypsy Poetry for soprano and piano.  At the 32nd Slovenian Music Days, she appeared with the Tartini String Quartet, performing works by Slavko Osterc and Marij Kogoj in arrangements by Alojz Srebotnjak. During the 69th Ljubljana Festival, she took part in Felix Mendelssohn Bartholdy's A Midsummer Night's Dream, under the artistic direction of Mate Bekavac.  
She has also appeared in a variety of operatic and oratorio productions in Slovenia, Italy, Germany, Serbia, Macedonia, Montenegro, Switzerland, and Croatia. As a member of Slovene Chamber Music Theatre, she has performed the roles of Zelmira in Gluck's opera The Deceived Judge, the Marquise Lucinda in Piccinni's comic opera The Girl from Cecchina (La Cecchina), and Milica in Ana Sokolovič's opera The Wedding (Svatba). The Italian composer Davide Antonio Pio invited her to take part in the world premiere of his original opera La Karneroika, in which she appeared as Donna di Trachis (the Woman of Trachis) in Ljubljana and Padua. 

She made her debut at the SNG Opera in balet Ljubljana (Slovene National Theatre Opera and Ballet Ljubljana) in 2012, as Musica in Monteverdi's L'Orfeo. In 2014, she was selected to join the Opera Studio of the same theatre, and during the 2014/2015 season she appeared as the Princess in Šavli's opera The Shepherd.  Since then, she has portrayed a wealth of operatic roles:  Susanna in Mozart's The Marriage of Figaro, Anne Frank in Frid's mono-opera The Diary of Anne Frank, Clorinda in Rossini's Cinderella (Cenerentola), Frasquita in Bizet's Carmen, Minerva in Offenbach's operetta Orpheus in the Underworld, Zerlina in Mozart's Don Giovanni, Felicia in Glass's The Beauty and the Beast (La Belle et la Bête), Esmeralda in Smetana's The Bartered Bride, Olympia in Offenbach's The Tales of Hoffmann, the Second Lady in Mozart's The Magic Flute, Giulietta in Bellinni's The Capulets and the Montagues, Giannetta in Donizetti's The Elixir of Love, Najade in Strauss's Ariadne on Naxos, Elvira in Rossini's The Italian Girl in Algiers, the Mouse Julija in Ajdič's Mice in the Opera House, Sophie in Massenet's Werther, Despina in Mozart's Così fan tutte, Nannetta in Verdi's Falstaff, and Adele in Strauss's The Bat. 

Štefica Grasselli is a member of the soloists' ensemble of the Slovene National Theatre Opera and Ballet Ljubljana and serves as a teaching assistant at the Vocal Department of the Academy of Music in Ljubljana.