Sylvan,
I am also responding differently than the other posters. You said you were having problems getting past the details, and I wanted to offer you a tool that is used with PTSD patients.
When one of these thoughts, or images, comes into your head, I'm guessing the first thing you do is tell it to go away, you don't want to have it. Unfortunately, our brains don't work that way - if I tell you not to think about a carrot, the first thing your brain does is pull up a picture, thought or experience of a carrot.
I had a horrifically traumatic event occur in my life that had begun to take over my waking hours. I could not seem to get it out of my head. I, too, have been in counseling for years and at the time had a wonderful therapist.
He explained that our brains get bored if we think about something long enough. That to get rid of a horrifying image or thought, the best way is NOT to tell it to go away, but to invite it to stay as long as it wants. In other words, when you have one of these images or thoughts or experiences, the way to make it stop is to close your eyes and immerse yourself in the experience. Look at all the details, feel all the feelings, relive it as realistically as you possibly can - and here's the important part - when you mind starts to drift away (as it will, because our brains also have fairly short attention spans), bring back that thought and make yourself think about it more. Make yourself focus on it until your mind becomes so bored with the concept that it simply won't focus on the situation anymore.
It isn't easy at first. It will probably involve some tears. It will hurt. But keep bringing it back into your mind. I promise you that once your brain gets bored with it, the emotional impact will go away. Then you'll be able to think about what happened without all the emotional baggage you currently have surrounding it.
One day you'll realize that it hasn't happened in a long time - and you'll have a reaction again, although it will be less intense. You'll need to repeat the 'focus until bored' exercise again, but it will take less time to become boring and the emotional factors will not be as strong.
You did not kill your mother, and you know this logically. You could not have prevented her death. You also know this logically. Unfortunately our brains aren't logical, and the emotions we attach to things aren't logical either. Thankfully, they do have a short attention span. Emotionally, our brains are not designed to stagnate, they are designed to move forward. You can speed the process up a bit and take advantage of your brain's fallibility to help yourself.
I hope this will help you find peace. I did not believe it could possibly work in my situation, but figured I had nothing to lose by trying it and was absolutely amazed at how well it did work.