What is the bad food you were previously feeding her?
How are you offering her the Nutri-Cal?
What is the new brand you are trying to get her to eat?
Try feeding her wet Solid Gold. It is just like people kind of canned tuna and it's stinkiness should coax her to eat (warm it up if it deosn't work). In the meantime it is a great quality food so if she still takes awhile eating her new brand of food, at least she is eating something. If she doesnt usually eat wet, she could have a bit of the runs, but you gotta get her eating something. Or at least drinking something if she isn't. Cats get dehydrated super fast and can go downhill quick. Wet food helps in this and it is also healthier, more like a natural raw diet, less fattening. Dry food has more carbs so if your cat is overweight you should really look into an all wet or mostly wet diet.
There is a really great cat forum just like as big as this one. I don't know if I am allowed to post it here, but it is for cats not a competing dog forum so I will post it and the mods can delete it if there is a problem. It is thecatsite.com ask your question there and you will get answers from a ton of cat people.