How do you write sacrificing her was a mistake a mistake that could have been avoided in a dashes for extra information

If im on the right track then a way to right it with dashes would be: Sacrificing her was a mistake-a mistake that could have been avoided. but i may not have understood the question??

Allusion and illusion. an allusion is an indirect reference, whereas an illusion is something that is unreal or incorrect. each of the nouns has a related verb form: allude “to refer indirectly to,” and illude (not a very common word), which may mean “to delude or deceive” or “to subject to an illusion.”