On insurance, while I certainly don’t know for sure, it is likely that the owner did not have loss of use insurance on the pony. If they did, the insurer would have been very picky about binding coverage and would have required copies of the radiographs from the PPE. The owner does not mention any insurance in the complaint, and if the insurer had paid on a loss of use claim, it would have subrogation rights to proceeds from the suit (the right to get their money back from any judgment or settlement). Presumably the pony had mortality and major medical, like most equine policies.
Looking at the policies on my horses, they do not have an affirmative provision requiring that only vets can administer medications. Instead, the policies exclude coverage for any loss caused by a medication or inoculation unless it was administered by or at the direction of a licensed vet and the vet certifies it was administered for preventative purposes or required by accident, injury, illness, or disease. So, you can give the horse the medication without a vet, but if it causes a problem, you may not have coverage.