To be blunt, the answer to this question is dependent on so many different variables it's impossible to give a precise answer. What was her upbringing? Did she live on a farm where animal death was a way of life? Was she brought up in a specific religion that extolled the sacredness of all life? Was she a conscientious vegetarian? Has she grown up in a world (or even a land) where capital punishment is still practised? If yes, are the executions public or private? If public, has she ever seen someone she cared about executed?
Does she suffer from some degree of pyschopathy? How intelligent is she? How well does she rationalise actions she finds morally reprehensible?
What is her support network like? How has she coped with the stresses of the past? Is she dependent on any legal or illicit drugs already?
The list goes on.
Put simply, just because someone has seen trauma before and dealt with it, it doesn't necessarily imply that she won't crack with new disruptive stimuli. Also, Maslow's Hierarchy of Needs also has a role to play here. Having to kill for your own survival will not have the same impact on one's psyche as killing to get that corner office you crave (unless you really are a psychopath to some degree).
When you talk to people who work in emergency service fields who see this kind of thing every day, they'll tell you that there are 2 types of people who go the distance and become great;
1) Those who can distance their emotions from their intellect
2) Those who feel the emotions but convert that energy to action
The simple truth is everyone is different. Those with a fight response (as opposed to flight) will probably fare better. Those who are exposed to this material constantly as a matter of survival will operate because they have no choice, but may fall apart later. Finally, there will always be those who are permanently scarred and will never be able to function under these kinds of stress. Your character? You really get to decide.