I'm so sorry to hear this, antigone. I was so hoping the little mare would turn a corner which would at least give you more options, but it wasn't to be.
Oh no I am so sorry bless you. None of this was your fault and I can well imagine how you must be feeling re your own pony:-('just truly tragic.
I agree maybe a call to charity just to explain the devastation that has been caused and hopefully preventing this from happening to another unfortunate person in the future. Tighter controls should and must be put in place. I know your situation was rare but just one case is one case too many IMO.