Well, here's another spin on it. As Jeannie has mentioned before, genetics can sometimes play a part in it. I was diagnosed about 6 years ago and I was 5'10, 170 lbs and under 10% body fat; low cholesteral and low blood pressure and yet...I WAS DIABETIC. I'm sure this came down through the genes and my poor eating habits and not enough sleep (18 hour work days) brought it on. HOWEVER, if you really really go after a Dr. Bernstein type diet (really low carb) and get some sort of exercise every day (I mean how hard is it to put on sneakers and walk for 45 mins after work) you have a good shot of keeping the Blood sugars normal. EXERCISE is key! If your weight is in line, the cholesteral, Blood pressure and all the other stuff tends to fall into place and VOILA, your body tends to take care of the glucose in your system. (TYPE 1's are the exception to this diatribe as they didn't get there through neglect and can't turn it around ).
If anything the scare the dietician put into you should MOTIVATE you to 1st read everyting you can about Diabetes and "Reversing Diabetes". This in turn should at least put you on a path to living a healthier lifestyle. Do this and you may very well escape her dire predictions!!! I only wish I know now what I did when I was younger or at the very least 1st diagnosed, but hindsight is 20-20.