Akuyaku Reijou wa Shaberimasen. Kakusei Shita Tensai Shoujo to Ushinawareta Hazu no Koma

They tried to silence her, but she doesn't need a voice to twist the odds in her favor. When Liliana wakes up in the body of an otome game villainess, she knows it's do or die. As the daughter of a duke and a candidate to marry the crown prince, she faces constant threats from assassins and her father's political enemies. Worse still, a fever has left her mute, unable to call for help or use magic to defend herself. Or so they all think! One quick attempt is all it takes for Liliana to shatter the common sense of her world, which dictates that incantations are mandatory for spellcasting. Now, all she needs to do is escape the grim destiny that awaits her. Though her foresight can only take her so far—the game doesn't start for another seven years—nothing can stop a six-year-old armed with erudition and cheat-level magic. (Source: J-Novel Club)