I am a diabetic who has walked the Camino from SJPP to Finisterre in 31 days.
I frequently return to the Camino. I am not an epxert but this is what I have learned.
My insulin was simply packed in the rucksack and it was fine. I always stored it on my right as the sun shines down upon you from the left!
There are cool bags that you can buy. Try the diabetes uk website.
If it is insulin I can post a bit more advice.
My other expeirience is that both doctors and hospitals exist all along the Camino, they are used to dealing with all sorts of medical issues. You may have to pay to see them, but they provide the safety net you need. I am amazed at how many pharmacies there are in comparison to Britain and even with my very limited Spanish I have coped. Its amazing what holding up a package or a bottle can do. If you need insulin you will need a doctor's prescription.
You can always get a taxi to the nearest large town or city to see a doctor and then get one back.
The only thing I do is that when I return I discard the insulin I carried as it will have started breaking down and even refrigerated it continues.
Check with your pharmicist how long they think insulin is stable at room temperature? One I spoke to said a couple of months.
Remember that freeszing some medicines is worse than keeping it at room temperature. DO NOT put it in the aircraft hold and be wary of placing it near frozen blocks of ice.
It is worth carrying a letter translated from English into Spanish saying what your wife's condition is, what medicine she takes, this is the phone and email of my doctor.
Any specific quesions?
In short, don't panic.