I know she's been finicky about foods, but would some peanut butter rolled in seeds help get calories into her? Of course the other girls will want some too...
This made me think that I do something like this in the winter for song birds (and, yes, my flock too, for a treat!) Take large pine cones (or use something similar), smear peanut butter on them, then roll in a mix of seeds (?& mealworms?), and put a string on them for hanging. These, too, won't last all week, but if you put up 3, so each gets a chance at some, it would give good protein and carb balance. You could also wrap some in wax paper and freeze and have your caretaker hang another set mid-week. It would be good calorie source for Minni, plus a bit of a boredom buster with limited free-run time.If she's eating any kind of seeds, those suet cakes are filled with seeds and can be hung so she has to work for them. Maybe you can find/make a mealworm/nut cake for extra protein for her.