Yes, definitely. Remember, she is a soldier. She also travels alongside the Doctor a lot, but has slightly different moralities than he does. In her opinion, the lesser evil is the better choice, no matter who dies on either side. After the war... Well, she saw the universe as 'kill or be killed'. She was never away from her blaster, and well, in my version of 'The End of the World', Cassandra didn't die by drying out.
What saddens me is that Rose rarely saw Jane's happier side, because she regenerated in the episode 'Doomsday'. However, Jane did give her life in that regeneration up to save Rose, which I think is really nice. Do note that I have no control over my characters, I am just a gateway to let them enter this universe.