rider gets hurt on owners horse and has no health insurance. Who is Responsible?

A girl at my barn has agreed to help train and sell my horse. She gets paid per ride and has been doing it for a month. THe other day my horse spooked and she fell off. Although she was not hurt, she did have some medical bills but she does not have health insurance. I have offered to pay for half but she is demanding that I pay the full bill. What sort of responsibility do I have for this?
--------------------
It may be different depending on where you live. Sometimes the owner of the property is responsible, sometimes the owner of the horse, and sometimes it's both. She is not responsible in this case. Unless you want to fight it out in court, just pay the full bill.
Source