I'm so sorry you're going through this. It's hard to have questions, to second guess yourself. It feels awful to believe you could have done something - or not done something - and things would be different. But you did the best you could with the information you had, and that's all anyone could ask for. Remember the good times you had with her, the love you shared, the beautiful life you gave her. Believe that the doctors were offering the treatment they thought was best, and that they have so much more education and knowledge of the benefits and risks of each option than most of the people posting sensationalized articles online.
I would urge you not to go to this psychic, because I worry that if the new puppy is in any way different from your old girl, you'll have to go through all this pain and grief again. Only this time, there's a puppy who needs you and doesn't understand that she isn't being who she was supposed to be. Absolutely take time to grieve, but try to do so with the goal to be able to move forward. Not to forget, not even to stop feeling the pain, but just to be able to remember her for her whole, amazing life with you again, and not just the bad parts at the end.
I believe our lost loved ones live on, in our memories, in what they taught us, in the impact they had on our lives. It's okay that you might not have that exact relationship with a dog - or any pet, or any living being - again, because just because you won't have her again doesn't mean you won't have something else some day that's different, but just as beautiful and brings you just as much joy.