Diabetes is not infectious or transmissible through sharing lancet, though sharing lancet is not recommended, as there are possible other diseases that could be shared (Ie. Hep B, if she had it, though still unlikely).
7.8 is about 140, which is about the maximum limit of normal, considering you just ate rice.
If you are concerned about diabetes, the best way to prevent it, or manage it if you already have it, is to restrict carbs (along with appropriate medications). Rice is a very high carb food.
Wishing you well.