First, I'm sorry Sophie Kate was not feeling well.
Hope she's getting all better!
Are you sure you need to fatten her up? I prefer a lean dog over an overweight one and I wouldn't really worry about it and just keep feeding her the normal amounts and she will get back to her normal size in time, I'm sure.
Jackson is 16lbs and eats 1/2 cup of Acana (it's about 430 kcal/cup). If he was eating a lower calorie food, I'd probably feed him 3/4 cup at most (with a bit of wet food). But, it depends on the food she's eating. I don't know, just for reference.
I have used the NB rolls before, I usually cut them up and use them as treats! I like NB as a brand.