Hi,
There's a grey area between 'normal' readings and 'diabetic readings.
If your results fall into that grey area, people often refer to you as a pre diabetic.
Not everyone considered pre-d goes on to become diabetic. Things like family history, lifestyle, other health factors and medication can all affect the outcome.
Since you now fall into the grey area, and have a diabetic sister, I would suggest you find out as much as you can about diabetes and low carb eating, and put in place some lifestyle changes now. They could have some real benefits in years to come, either slowing down the development of the disease, or stopping it from developing in the first place.
Good luck!