I usually add 1 cup of Skim Milk to my before bed shake, but it has 12g of sugar, should I be worried about getting an insulin spike from this before bed?
Firstly milk has 12g of lactose; sugars are not all the same.
Secondly, the focus on insulin has been blown way out of proportion IMO. Insulin itself is not a cause but an effect. Just because a certain food raises insulin more than another does not necessarily make it good or bad. Cottage cheese seems to be higher on the insulin index yet it is frequently recommended as a nightime meal for its slow releasing protein. Insulin facilitates glucose metabolism, increases protein synthesis, and increases fat storage. The question is which is the insulin affecting the most - where are the nutrients actually going. Just because a food is high GI or Insulin index does not mean it will make you fat.
In short, there is no reason to avoid milk as long as it fits into your calorie and macronutrient plan (you do have a plan right?). It is a low GI whole food with some good nutrition.