The best treatment for her skin itching really depends on the cause. Most causes of skin itching are unrelated to diabetes. Allergic reactions can cause itching because of histamine release. Skin infections with fungi or parasites such as scabies can cause severe itching in different parts of the body. These are best treated by treating the cause, but symptomatically can be helped with antihistamines such as Benadryl.
With that said diabetes can result in nerve damage which can manifest as pain, burning, and sometimes itching. This nerve damage takes place first in the feet and hands and progresses towards the body. If this is the area where she is itching then the diabetes is likely related. If this is the case, then good blood sugar control is the first step towards relieving her symptoms. In addition medications such as gabapentin (Neurontin) can be very effective at treating this type of discomfort.
I suggest that you schedule an appointment for your wife with her primary care physician
. He or she can determine what is causing this itching and make sure that no complications such as skin infections have happened because of her scratching. If the itching is not due to diabetes, then your wife may warrant a referral to a dermatologist
for further evaluation and treatment.