Add fats and protein. Veggies won’t keep you full as long. Avocado, hummus, eggs, jerky. Eggs are super handy as you can make a batch of something like frittata and cut it into squares, or boil a dozen eggs, peel and put in a tub of water and they’ll be easy to ‘grab and gobble’

Protein. Nuts, jerky, eggs, fish,

Turkey jerky or beef jerky. Smoothies w/ peanut butter, milk (or coconut milk) and fruit, protein powder.

Homemade muffins w/ fruit or veggies in them.

Sushi, hard boiled eggs, fruit with Greek yoghurt and nuts are filling snacks.

From experience don’t just say “eat an apple if you’re hungry” to a ravenous child/tween after swimming for hours! The thought of apples still makes me queasy.

Milkshakes lol fat, protein, carbs

Feed the poor young woman some more calories! Fat for satiety. Low GI carbs for longevity. Soft cheese on crackers for example. Oaty flapjack biscuits (not the US kind). Protein shake once a day. I know you can't tell from threads but it sounds like you don't believe her hunger and you are more worried about her getting fat than keeping her fuelled.

Make an extra meal or two a week that you don’t serve for dinner. Then it’s available for lunches and snacks.

Full fat Greek yogurt with granola, chocolate milk shake made with full fat milk, cheese bean burritos (hot, or cold and wrapped), cheese sticks and crackers, cheese and ham toasties (again hot, or cold and wrapped).