Sounds like a serious infection has got hold of her. It can take many weeks for this to be resolved. She isn't awake because they are keeping her sedated. Haven't they told you anything?
Is she being ventilated by machine? or is she breathing by herself?
I am sorry to hear that your sister still hasn't woken from her surgery.
I am from the Netherlands and as far as I know there are not much differences in used techniques in Germany/Netherlands compared to other developed country.
What does make a difference is the setting in which the surgery is done.
In an emergency situation, risks are much higher and complications more often happen, compared to a well planned and prepared surgery.