In the mirror universe, T'Pel was a Vulcan female who lived during the 23rd and 24th centuries. She was the wife of Tuvok and the mother of Sek, Varith, Elieth and Asil. She and her family lived under oppression from the Klingon-Cardassian Alliance.
Her oldest son, Sek, died of an infection in the 2360s, though a Cardassian physician had tried hard to save him. She and the rest of her family were considered officially dead and murdered by the Alliance. The truth was that her children had gone underground and Tuvok and T'Pel both joined the Terran Rebellion. Though Tuvok became an active member, she lived in Memory Omega on Regula 1, where she rarely contacted her husband for fear of being exposed to the Alliance.
T'Pel was summoned by Tuvok when he was separated from the rest of his group and aided him in rescuing Kes from the Alliance, she and Tuvok trained Kes to hone her abilities and use them against the Alliance. (VOY - Mirror Universe novel: The Mirror-Scaled Serpent)