Augh!!!!
I am so sorry about your Kiwi. I know what you are going through. Images like that stay in our mind and its hard when that is the last thing we can see of our beloved. I am sure you felt so helpless! And its normal to go through all the stages of grieving - even for a little bird - as if it where a close human friend. I recently lost my cat... well if September is recently. And the "what if's..." never seem to stop coming up. But neither do all the happy memories I have of her.
Remember the good - I have no doubt she is flying above the clouds, looking down on you, sending her beaky kisses and loving reassurance that you did all you could. She knows.