Everything we know about sacrifice we learned from Creed's classic butt-rock anthem "My Sacrifice"—until The Martian came along, at least. The novel is filled with instances of people sacrificing something important to them for the sake of others, whether we're talking about NASA's massive budgetary sacrifices or the very personal ones of the Hermes crew. There might be some parallel universe out there where Mark gets stuck on Mars and everyone is too busy playing Candy Crush to notice, but we can guarantee that's not happening here. If anything, the novel shows us that the desire to give up our well-being for the sake of others is hard-wired into our DNA.
Questions About Sacrifice
Why does Commander Lewis feel so guilty about leaving Mark behind?
In what ways does NASA make sacrifices so Mark can survive?
Does Mark make any sacrifices of note?
How does the family of the Hermes crew respond to them returning to save Mark?
Chew on This
Though the personal sacrifices made by the Ares 3 crew are impressive, there's nothing more surprising a big government agency like NASA giving up so much money and time for one man.
Basically, Commander Lewis is so guilty about leaving Mark behind because she believes that she should've sacrificed herself for the crew.