Let a roaring fire die down then stir the remaining structure and ashes apart with the stick that has been sitting in the water bucket and hand sprinkle with water---do not pour the bucket of water on the fire. Repeat until a hand is passed over the fire circle, several inches above, and no warmth from wood pieces or ash is felt anywhere in the fire circle.
Camp stoves, elevated charcoal fires, and no-cook are now recommended for the preparation of meals. There also has been a shift of focus in Girl Scout camping trips to spend less time on meal preparation and more time on other outdoor activities. Use of wood fires for evening campfire activities should be limited to once during a camping trip with a small fire for a short length of time. These adjustments allow girls to still have an occasional campfire while greatly decreasing the impact on the environment.
Always check with local authorities to learn if campfires, both wood and coal, are permitted. The following are good sources of information: official government websites, local nature groups, Facebook pages run by official organizations, local MWR specialists, local park rangers, guides or conservationists.
Always follow Safety Activity Checkpoints and Outdoor Education in Girl Scouting when working with fire.