Well... she really succeeded with changing Quarian´s mood, Shepard thought, from one loss to another. And this one looked even more personal. Death of her crew surely was terrible and mind breaking, but the loss of a friend was a quite different thing. She could at least blame someone for deaths on the ship. She could turn her grief into something more useful, like anger. She could turn her sadness into an edge and turn that edge against Saren and Geth.
At least Shepard did so, after Mindoir. She had never really mourned the death of her parents nor friends. It took her months just to truly admit that they are not going to return. Only thing she could think on was how to make the slavers pay, so that no other person had to ever endure things that she did.
Loosing friend in a way described by Zeto had to be a lot worse in certain ways, more torturing. Shepard lost a lot of person she knew, but it was always fast. In one second they lived and in another they didn´t. It was fast, simple.
To watch your friend die, in course of days, or weeks maybe, had to be far more painful.

Shepard didn´t really know what to say. It was hard for her, to talk about these things.
"I am sorry for your loss," she just said. It was cheap, but she didn´t find anything that would fit better. 
"Sometimes, I wish that we humans lived as long as Asari do or were as resilient as Krogans are. It would be so liberating to live that long without fear of imminent death."