Everyone has their own special treasure, ranging from sentimental items or a precious person. To Shepard it was always her 'family' ranging from EDI all the way to Coretz. They were always there, helping her along the way, but Mordin was always different for her. How he greeted her, how he knew how to cheer her up under stressful times, and how he would be the shoulder she needed to cry on. No one had lost something of a precious treasure, and every second of the war she prays that she will never know that feeling of losing something important.