What a horrible thing to have happen! I can sympathize - I know what it's like to lose a horse in an unnatural way. As morbid as it sounds, I'm glad it was instantaneous, and she felt no pain. She'll be patiently waiting for you on the other side of the Rainbow Bridge.
Your story is so very sad and I can imagine just how guilty you feel over such a tragic event. I recently lost three horses to a fire. Before investigation some speculated it was my fault or electrical. No matter how the fire happened, Iíll always blame myself for not saving them or preventing the fire in the first place.
I imagine that even if you had been perfect you would still harbor regret and blame yourself in some way. A friend of mine suffered a similar tragedy as you only in her case some evil person, cut the fence and apparently either tried to walk the horse away from her property to steal him or did it out of cruelty. The horse was struck by a car and found to have a rope around his neck. My friend was on the scene for over forty minutes watching as her horse suffered with broken legs and internal injuries before the police shot him in the head. Sometimes thereís no way to circumvent heartbreak.
I donít think I will ever sleep without having a horse nightmare unless I adopt another needy horse from the US Bureau of Land Management. Try to think of the happy times you had with your horse and what a good life you gave her. Iíll bet your horse never turned away from you and to her the sound of your voice was like the chiming of little bells.