She does still go to the doctor yearly for tests. I will have her look into those suggestions. Maybe a new doctor is needed. She has seen 2-3 different ones but maybe they missed something.
Also try this as it can not hurt. Go get an over-the-counter blood glucose testing device (they are now about $9 in walmart) and check your wife's blood sugar throughout the day and see where it is.
In the event her blood sugar is abnormally high, this adds a tremendous amount of stress on her reproductive system. She may not have a yeast infection, but her immune system that keeps everything in check may not be able to function normally. This could result in a constant imbalance of her natural bacteria that cause her to be chronically irritated.
It can not hurt to check her blood sugar and find out that it is normal. You can also check your blood sugar as well. The chance one of you would discover that there is a problem would drastically improve you ability to begin making some lifestyle changes and become much more healthy.
As a side note, I do not know what kind of lube you are using, but if you have never tried coconut oil (the kind you buy at the grocery store to cook with) to help alleviate some of her issues, you should definitely try that. Apply some regularly to her, even if you have to do so in a nonsexual context. This should help her not feel so irritated and perhaps help that area of her body to become more healthy and receptive to normal lovemaking.
The two of you should read up on coconut oil and the vagina together. You can find all sorts of testimonials about it all over the internet. If she suffers from any type of imbalance that causes irritation, this should help.