Thanks for your reply, an interesting question you ask about Selenium and Vit e !
Selenium is more associated with a cows metabolism and the only way to find out if your girl is deficient is by your vet doing an expensive test, if you feed her cake [pellets etc], grain and or vit/mins check the packaging to see what is included. Selenium should be included as a matter of course, you might like to Read here
for more details.
Vitamin E is of course equally vital, because it is a natural biological antioxidant you might do as well to try rubbing in some [in oil/cream form] into her udder/quarter to aid healing and skin recovery. Also check any feed products to see if it is included in them.
Do you have any disposable/latex gloves, if so try and use them any time you touch her udder and destroy them after use.
Is it possible to show a photo of her udder ? It would help us to help you better.
Good luck !