Wife has always had fasting blood glucose in the mid-80s. She had A1c done and it was 5.7. Reason for concern? Had very stressful 2 months prior.

No. A fasting glucose in the mid 80's and an hga1c of 5.7 are both totally normal results. Should not be a concern unless there are other health issues. The stress, however, could be more of a concern if not handled properly.
Glucose is. Normal, but if she's overweight it will get worse over time -- so diet, exercise and weight loss are important to do now rather than waiting until something happens.