What is the best food to gain weight for girls?

Balanced nutrition: I know of no persons that want to gain fat. Most would like increased lean muscle mass & that requires the balanced nutrition as proposed by a clinical dietitian. No one food would provide what is needed. Food alone without exercise & proper rest would also not help. If you just want to gain weight & don't care where it goes eat anything that appeals to you.

Weight gain: Make sure that weight gain is medically indicated first. Foods to help with healthy weight gain: almonds, cashews, pecans, sunflower seeds, flax seeds, walnuts, hummus, avocados, granola, trail mix, dried fruits, extra virgin olive oil, canola oil, protein shakes, protein bars, lean meats, poultry, fish, Smoothies (with added silken tofu or powdered milk), Greek yogurt (full –fat), pasta/ bagel

Why?: Why do you want to gain weight? If you are otherwise healthy but just skinny, let it be. You will gain weight as you grow older and then you will look back fondly at this time when you could eat and not get fat. If you overeat to gain weight, just remember the weight may not go to places that you want to enhance. Wish you good health!