A PA protection from abuse order prevents the defendant from ANY contact with you whether that be at your home, work, school, public places and doctor offices. If the defendant appears at the appointment, you are entitled to telephone the police and seek an order for Indirect Criminal Contempt of the domestic violence order and, perhaps, have him arrested. My best advice is to inform the psychologist of the PFA order and I'm sure the psychologist will warn him not to appear.
On the other hand, because you have physical custody of your child does not necessarily mean that the PFA order granted you legal custody which is the right to make decisions for your child involving medical care amongst other things. If you are taking your child to a psychologist for the first time, you should make certain that you have legal custody rights pursuant to the PFA and the right to take him to the Dr. appointment.
You should contact the attorney or legal advocate that assisted you with the PFA action to clarify your legal custody rights.
The suggestions made are intended to inform and not advise and are based upon general statements of PA laws and specific events or facts may alter the law. You should contact an experienced PA family law attorney for specific legal advice regarding your issue.