Hi! Had gestational diabetes with all 3 of my pregnancies -- I'm sorry you're having to deal with one more obstacle when it sounds like you've had more than enough already, but the diet is so healthy that it's actually a good thing for both you and the babies. You'll keep weight gain at a good level and it will help after delivery as you will have established good habits. :-)
The diabetic diet is about limiting carbs to an acceptable level to avoid spikes in glucose -- not just the regular carbs you think of, but also starchy vegetables (corn, peas, potatoes, etc.), so while eating some is good for variety and nutrients, you'll need to limit those. It's also helpful to combine protein and carbohydrates, as the slower-digesting protein will help keep the carbs from digesting too quickly and causing a spike. Also, fruits are ok (but in set quantities) but avoid fruit juices -- the natural sugar in juices can really raise your blood sugar, while the whole fruit has the added fiber benefit. My dietician also told me to continue using regular salad dressings, because the low-fat variety has added sugar.
Like Jennifer said above, the walking (if you're allowed to) is a great help -- 30 minutes of walking after eating will reduce blood sugar levels quite nicely. :-)
Best of luck to you!