As wonderful a drug as metformin is, nothing compares to 'lifestyle changes' to bring blood glucose levels down and your liver and your pancreas functioning normally again. I am shocked that your wife's doctor did not say this to her. 'Lifestyle changes' of course is a funny little phrase for avoiding and eliminating sugar and processed food in your diet, and moving those limbs more and getting out and about on a walk and whatever. Perhaps her doctor decided for her that she could not or would not do either of those things? (Even if that is so, I am still shocked.)
Two books that I read about on this forum are fabulous for prediabetics in particular - 'The Diabetes Miracle: 3 simple steps to prevent and control diabetes and regain your health...permanently' by Diane Kress, and the wonderful 'Dr Bernstein's Diabetes Solution:The Complete Guide to Achieving Normal Blood Sugars' by Richard K Bernstein. Another really good easy to read one (the layout is fabulous) is Dr Hyman's 'The Blood Sugar Solution: The best-selling program for preventing disease, losing weight, and feeling great'.
When I first got diagnosed with T2D I envied prediabetics! The road is so short from a , for example, 42 or 44 HBA1cs to 40 and below! Now I have a greater understanding, as a prediabetic now myself, that it's all relative - and that road can still seem mighty long and hard to go down even so. I'm at 44 and 40 and below seems a long long long way off. I wish your wife the best! And hope she gets some good stuff out of those very good books on the subject, that will work for her.