She unintentionally knocked the file off the table, and saw the photo of her husband and the mistress.
Examples (Wiktionary)
Mandarin
他招认，当时他的这一不经意的行动，是因为生怕如果金正恩同志的领军基础和体系一旦巩固起来，将给他篡夺党和国家的权力造成巨大障碍。
他招認，當時他的這一不經意的行動，是因為生怕如果金正恩同志的領軍基礎和體系一旦鞏固起來，將給他篡奪黨和國家的權力造成巨大障礙。
tā zhāo rèn ， dāng shí tā de zhè yī bù jīng yì de xíng dòng ， shì yīn wèi shēng pà rú guǒ jīn zhèn gēn tóng zhì de lǐng jūn jī chǔ hé tǐ xì yī dàn gǒng gù qǐ lái ， jiāng gěi tā cuàn duó dǎng hé guó jiā de quán lì zào chéng jù dà zhàn gài ．
Jang confessed that he behaved so at that time as a knee-jerk reaction as he thought that if Kim Jong Un's base and system for leading the army were consolidated, this would lay a stumbling block in his way of grabbing the power of the party and state.