Disclaimer- I am NOT a lawyer.
I am however, a Registered Nurse. The idiot woman deserves to be disciplined by the Board of Nursing, at the very least. Contact the board of your state, most of them have websites, and file a complaint. Good Samaritan laws do not apply to medical professionals in some states (help me out, EMT professionals), and she is held to a higher standard of care, which she violated. A counter suit should cool her jets, and the loss of her nursing license would cost her a great deal more than she could gain from this frivolous lawsuit.
Glad you are okay, sorry you have to deal with this aggravation.
JoeBob
After thinkiing about this for a few more minutes, she commited assault and battery when she slapped you around.
Have you considered filing charges? That would get her in a bunch of trouble, professionally.