I really doubt spending a whole thread saying "I told you so" is really going to do more than make her feel completely horrid about something sh has no control over.
She asks for advice time and time and time and time and time again and ignores it. And then is all 'oh my, my pony is hurt, so shocking'.
She needs to feel horrid. It is her fault.
If her parents will not come thru then sell the horse so it has a chance at a healthy life with a responsible owner.
This is not rocket science.
Who the heck is PO, BTW? You keep saying PO.
Not true, my vet at the time INSISTED that the person paying the bill be present at all exams so that he could get THEIR consent on how to proceed with treatment. I understand any vet who does this because of course any KID is going to agree to all sorts of treatment for their beloved horse and then the parent NOT pay the bill because the child said yes to the most expensive route of treatment.