In describing the trenches, you would want to explain to her that these were dug into the ground and ran for great distances, with tunnels connecting larger below-ground-level areas. Mention that they were crowded with men, guns and ammunition, backpacks of clothing and other equipment. Tell her how water and snow collects in the bottom of the trenches so that they become muddy; try to make her understand how cold and wet and miserable it feels to try to eat and sleep and get ready to fight in them.
Help her to get a picture of looking over the top of the tunnel, through the rows of barbed wire stretched along the length of the tunnels, across no-man's land, and into the barbed wire standing along the near edge of the German trenches. Comment on the difficulty of judging distances between trenches or fences in the very snowy conditions under which the Battle of Vimy Ridge was fought.