Thank you all so much for your input and kind words.
When the injury occurred, I couldn't get a vet to come out until the next day, even though I stated very clearly that it was an EMERGENCY and that the filly needed to be euthanized. The vet who had been treating her would not come out. All of the vets stated that they were "booked", which for some reason took priority over a horse who was missing pieces of her leg.
Please don't judge me for this, but the only recourse was to have her humanely shot. It was my vet office who recommended this man and he knew what he was doing. His business was the removal of carcasses and he had euthanized hundreds of large animals over the years.
There was no way that I could let her suffer like that for 18 hours. Additionally, she could have broken out of the round pen panels before morning, since she had already jumped through one before. While the idea really bothered me at first, I remembered several tragic vet-done botched euthanasias that friends had experienced. One friend's horse flipped when being euthanized and almost crushed my friend. Another friend's horse was dying and the vet couldn't find a vein. The horse was thrashing around violently and groaning, but the vet couldn't put him out of his misery and he died a horrible death. Sadly, that horse had impaled himself on a wooden post. Yet another friend's horse took 45 minutes to die, even though the vet gave several fatal doses.
The man who shot her told me that he knew a number of vets who had been seriously injured when trying to euthanize horses. He was good. He places a container of sweet feed on the ground for the horse. She was kept in the pen for safety's sake and she never knew what hit or or felt fear.
My vet probably didn't want to euthanize this filly because she already knew that the filly was a handful. When trying to remove the drain from her chest, she had to be heavily sedated and even accomplishing that was extremely difficult. She reared after the needle was inserted and yet again after only part of the sedative was administered. We had a tough time holding her even after she was partially sedated and had to go through the whole process again before she could be doctored, with her getting progressively more difficult.
It would have been very dangerous for all concerned to try to euthanize this mare by injection, so in the end I was glad that I couldn't get a vet out. Again, please don't attack me for this. There was no choice in the matter. Being shot made a necropsy of her brain a mute point, but I would have liked to have one done.
After being threatened with a lawsuit, the breeder did return the purchase price within three days of the filly's arrival. However, due to vet bills, fencing costs,and related expenses, I am out almost $2000. My friends agree with those of you who believe the breeder knew all about this filly's issues. It is beyond belief to me that anyone would risk so many lives and put this poor filly through so much stress by putting her on a transport, when she should have been euthanized by them.
Sorry to ramble. Haven't been sleeping worth a darn and am really worn down. Thank you all so much for your time, your input and kind words. For those of you who dealt with similar young horses, thank you for sharing your experiences.