who never killed somebody in her whole life is
Many of those who participated in the Holocaust and other crimes never personally killed someone, yet helped to make sure that the killing happened as efficient as possible. I made it clear that I would have prefered it if - at least the higher ups who ordered the shooting of refugees - had been charged with murder, but that is not for me to decide. We live under the rule of law. The courts decided that what happened at Stutthof is murder and genocide, while the guards at the Berlin Wall are guilty of manslaughter. If you are guilty of assisting of the former, you will be judged more severely.
but the Wehrmacht soldier couldn't?
You are comparing cases that are not really comparable. One, it is not like the ones killing refugees got "excused" for following orders. It was acknowledged that they lived under conditions that made it more difficult to disobey (we know that border guards were threatened with punishments if refugees escaped, while Wehrmacht soldiers had nothing to fear when they refused participating in war crimes), but they nevertheless received some sort of punishment. Serving in the Wehrmacht itself is not a punisheable offence since drafted soldiers had no choice in the matter, but if someone living today could be proven to have participated in specific crimes, he could be charged for them. But since this is difficult to prove, the courts have decided to charge those who specifically worked at KZs where work was voluntary and the killing intent obvious. If you worked there, you knew what the purpose and your role was. Someone like Oskar Groening freely admitted this.
Imagine for example, that 70 years ago two men abducted children. One of them guards the children while the other gives the orders and organizes the whole kidnapping and murders. A third one, a woman, is writting down the orders and sends them to the guy who guards the children. The contents is explicite, she knows children are dying, she witnessed the abuse of the children herself and she has written letters in which the man in charge talks about the tools they need to kill children and make the bodiesdisappear. She writes down letters in which the murder of children is even ordered. She does this "work" for years. Would you hesitate to charge her for assistance to murder, even many years later?