what a horrible thing for you to have to deal with
Personally I always travel with rear top doors open and without a partition - have done for years with no incidents so please do not think you were acting out of the ordinary
One thing I HAVE to ask - what make and model was your trailer?
It is a Westwood Trailer Hunter 505 Style. It was not even two years old and now we are thinking of changing it. I have read that horses prefer being transported in boxes that allow them to stand at a 45 degree angle to the car. And, i have seen boxes that are a lot brighter on the inside.
That is very sad. As you didn't have partition in your trailer she would have naturally been able to stand at 45 degrees is she had wanted to, so a different trailer wouldn't have made a difference.