u/Improvement_Lonely

So I'm writing a dark fantasy story where my female character and her people are being attacked by another kingdom and it's like an ongoing war where the female leads kingdom is at a huge loss and is going barren due to continuous attack. So in this scene the female leads mother gets attacked and gets beheaded by one of the knights.

Since the death and the gruesome scene gives a huge impact on the fls life, I want to write a nightmare she gets of her mother and I'm confused on how I can write a nightmare sequence and make it seem that nightmare is realistic??