Hypoglycemia (low blood sugar) Support Group
The term hypoglycemia literally means "low blood sugar." Hypoglycemia can produce a variety of symptoms and effects but the principal problems arise from an inadequate supply of glucose as fuel to the brain, resulting in impairment of function. Derangements of function can range from vaguely "feeling bad" to coma and in the worst case, can be fatal.
A fruit smoothie, if it's the sort you buy at the mall and not the kind you make yourself, can be pretty big and full of sugar. If I ate one of those, I would not be ready to eat another meal in an hour. If I were planning to eat dinner with someone and I saw them drinking a smoothie just an hour before, I'd think that they didn't care too much for our dinner plans. So stick to something small and healthy, reminding her that you have a medical need to control your blood sugar, and she should be cool with it.
It sounds like your girlfriend has a lot to do, with taking care of the baby and also having to figure out what two adults will eat for dinner. Maybe you could help her out with whatever tasks need to be done before you can eat dinner, so you can both sit down to eat sooner. If your small healthy snack gives you energy to help out with some of the pre-dinner chores, your girlfriend will be much more understanding.