Haha, yeah, she's an amazing cook, but before going primal, we'd use a teaspoon of raw sugar in tomato sauces to balance the acidity, so she just substituted the stevia for it. She never measures the amount of ingredients she uses, but I deduced that she used about a teaspoon of stevia.
Lesson learned, and I ate the original meal, anyway - it was edible without the squash, it just tasted like sweet sauce and meatballs.
You can also use a couple kernels of fresh sweet corn to balance out the sauce, works really well!