I'm so sorry to hear this. Assuming that the news is what you expect and dread, know that there have been so many here who have been through what you are going through. There are some threads that you can look at that will help.
http://www.rottweiler.net/forums/vet...decisions.html http://www.rottweiler.net/forums/vet...-dog-down.html
Rotties are very stoic dogs and eager to be with us and please us, so they don't show the pain they are really in. She has always trusted you to take care of her and do what is best for her. She has no sense of time, so she doesn't think, "maybe I will feel better tomorrow". Dogs live in the here and now.
Love her, spoil her, take some pictures, make some lovely memories, and when it is time, let her keep her dignity and go to the Bridge in the place she has always felt safest.... in your arms. You have given her a wonderful life, and she has returned that gift tenfold. Letting our beloved ones escape their pain is the one time we come close to showing them the selfless love they show us every day.