Born in Niederkorn, Luxembourg, Steil-Antoni was taught to play chess by her father when she was nine years old.

[1] In 2006, at the Women's Chess Olympiad in Turin, she won the individual gold medal on board two thanks to a score of 10/12 points.

Steil-Antoni tied for 2nd–3rd places with Pauline Guichard in the WGM tournament of the Condom Chess Festival in 2008, finishing second on tiebreak score.

[7][better source needed] She finished second in the Klaksvík Open 2010,[8] the Uxbridge e2e4 Autumn Women's International in 2010,[9] and the WIM tournament of the Mulhouse Chess Festival 2012.

[citation needed] Steil-Antoni currently plays for The Smashing Pawns (Luxembourg), Vandoeuvre (France) and Cheddleton (England) clubs.