Silvia was not a woman to be easily intimidated. She had been through her fair share of combat on the battlefield, where blood and death were commonplace; however, Desmond terrified her.
The reason was straightforward, Desmond was not a variable, an obstacle, or a threat that could be avoided. Silvia was smart enough to understand that with the difference between them, Desmond could crush her like he was dealing with an ant.
As Desmond's right-hand man within the military, Silvia knew more about Desmond than most and had interacted with him personally, so she understood the kind of man Desmond was.
In essence, Desmond dealt with people in four different ways, each depending on how Desmond perceived said person. Long story short, in Desmond's mind, there were only four types of people. Those that Desmond perceived as family, tools, obstacles, and those that he viewed as enemies.