Does she know her weight Betty? I tend to advocate blind weighing as it has been so important in my dds recovery. Unless you are certain that she understands she will have to gain weight and won't then freak out and restrict further I'd blind weigh.
The sachets are a very small portion so I triple it with normal porridge oats.
Soups are great for getting calories in, I make a tomato and pepper soup which is tomatoes and chopped up peppers and an onion fried on oil, then blitzed, add double cream and stock and serve with crusty bread and butter. Really yummy 😋
Other good foods that soak up calories are scrambled eggs, use duck eggs and mix in butter and double cream.
Potatoes, they soak up butter and cream really well. I make a mash potato and add cream, butter and cheese to it.
Anything with a sauce, I make a salmon pasta dish in a white sauce. The white sauce in butter, flour, double cream, soft cheese and hard cheese and add stock to taste. Also pesto - add extra oil is good on calories.
Avocado oil is very calorific but it does turn food green!
With lunch and dinner I've always insisted on a main and a pudding. With lunch this tends to be two large tuna Mayo rolls with a packet of cheddars for main, pudding would be a yogurt or a small piece of cake.
Also slowly increase portion sizes, I have done this gradually throughout and dd has never noticed (or if she has not commented!)