In the beginning, when she was still fighting at the frontlines, the killing curses weren’t used quite so prominently. But the injuries were vicious and healers were needed. That’s when she switched to becoming a healer and potion maker. She didn’t see Death Eaters on the field anymore. She just saw what they did to their opponents. The longer the war went on, the more brutal the injuries were. While her potions got better at healing injuries, Voldemort created more heinous weapons.