Tinker, best advice on diet and lifestyle at the moment (based on what I've read in medical textbboks and Diabetes UK's literature) would be:
Avoid becoming overweight (aim for body mass index of less than 25).
Eat a low-fat, high carbohydrate diet. My dh's dietitian's advice was to follow the guide of imagining your plate is divided into different sections. The meat part of your meal should take up no more than a quarter of your plate and the rest should be half staple and half vegetables. Things like cakes and biscuits should really be only eaten as an occasional treat
Try to stay reasonably fit.
Apart from this, I'd say just be aware of the symptoms of diabetes so you can get treatment early on if it does develop. For my dh it was thirst. It's thought that lots of people develop Type 2 diabetes many years before they are diagnosed, because the symptoms develop gradually, and during this time of course lots of damage to nerves, eyesight etc. can occur.
After dh's diagnosis, he was put straight onto tablets (metformin), but in the first 6 months he managed to lose 2.5 stone by dieting and exercising (taking him from BMI of 27 to BMI of 24) and after he'd lost the weight he was able to come off the pills and now he just has to be careful with his diet. I'm not saying everyone would see such a huge improvement just by losing weight, or indeed would avoid developing diabetes by not becoming overweight in the first place. But it can make a lot of difference.
Hope your mother is doing OK and not finding the diagnosis too overwhelming. I felt quite depressed at first, to think that dh had such a serious health problem (it didn't seem to bother him though!). Now I feel OK about it because he is controlling it so well and there's a lot of research going on into new treatments. This could be important for him because we've been told that he may well need to go back onto medication as he gets older as it's a progressive disease.
HTH.