I was diagnosed while already with my boyfriend, I don't know if that's made a difference or not. But carb counts with me, I tell him my BG (he sometimes asks... But usually I announce it anyway. Makes me feel better to share it ) I haven't had a bad hypo yet but I know he'd be there for me when I do. He's had a steep learning curve at the same time as I did.
You need to help your girlfriend learn what to expect. I'm sure she'll be supportive once she has grasped the basic concepts at least!