I'm so very sorry, I know there are no words. I've lost three rabbits and it seems that beyond the obvious sadness and loss, a common theme is that we question whether we did enough, did too much, should've done something else, etc. I think it's because they are so fragile and it's so hard to tell what's going on with them. Things never seen to be as clear-cut with rabbits.
If it's any comfort, I don't think your bunny was scared without you when she passed. I'm more familiar with human deaths, but in my experience once any living being is near death, they don't really register their surroundings. And it sounds like she didn't suffer since they thought she was doing ok. The same thing happened to one of my rabbits. They thought she would be going home soon, then she suddenly died on the ultrasound table. She had a blockage too.
You gave her a wonderful life and she knew she was very loved. And you did everything you could to help her. Please try to remember that- I know how difficult this is. Again, I'm so sorry.