With all due respect to your MIL, unless she's a Certified Diabetes Educator or Endocrinologist, she likely doesn't have the training to make suggestions regarding your gestational diabetes.
Controlling diabetes goes well beyond what you're eating. What have your numbers been if you're saying they're too low? Different people experience symptoms of hypoglycemia at different levels. The normal person should keep their glucose levels between 90-110 fasting. Numbers following meals (called postprandial glucose levels) can be up to 140 to be compliant with recommendations from the American Academy of Clinical Endocrinologists (AACE).
I'd call your local hospital and ask if they have a Certified Diabetes Educator and ask the question to them. In addition to your meals, your liver is a source of glucose during the day. Your pancreas produced a hormone called glucagon that signals the liver to produce and release glucose when you're low. It's a natural function that often results in many patients having higher than normal glucose levels despite taking medication correctly/eating well.
Also, when are you testing? It's important because if it's too close to meals, it may really skew the results.
I'm not a certified diabetes educator, but I did sell insulin and other hormone-based diabetes medications for 8 years, and I know the disease well.
In addition to calling your local hospital (you should be able to speak with an educator immediately), you can check to see what resources are available on the following site (American Academy of Diabetes Educators):
http://www.diabeteseducator.org/search.html
Good luck!