is it mange

Question
my rottweiller has scratched the hair of one eye until it bleeds swells up  gets infected has eaten its tail to a bloody stump and has now started on her rump.

Answer
I am not sure what you mean about "scratched the hair of one eye" but if she is scratching that vigorously it sounds like she has a bad case of fleas.
Dogs don't scratch at mange that much although they can. It is more tell-tale that it is mange by big patches that form which are bald,patchy looking and usually red and sometimes weepy.
The most common places for them to get it are on the head, neck and chest areas- then it spreads all over the dog.
You have to get a skin scraping done at the vets to diagnose it properly.
But the most common cause of what you are describing is fleas, plain and simple.