Can I sue a person who filed a civil action against me for "harassment" based on conduct in the course of litigation

Generally, one cannot sue a person who filed a civil action against you for "harassment" based on conduct in the course of litigation. The court may sanction a party for harassing conduct. Someone who repeatedly files meritless civil actions against you may evtentually be declared a vexatious litigant. If someone files an abusive civil action for an improper alterior motive, you may possibly be able to file a civil action against her for abuse of process. You should consult with an attorney to discuss the particulars of your matter and for any specific legal advice.

If the harassment is about something other than the lawsuit then of course you can sue them. if you are talking about an anti harassment restraining order then you can ask the judge to make any finding mutual.

Your facts are not clear. I am going to assume that you sued the "harasser" and she has now sued you for malicious prosecution after you lost your original lawsuit against her. Is this your situation? If so, you cannot sue her for "harassing" you by suing you.

If her "harassment" consists of something other than filing the suit against you, then maybe you can sue. If she has sued you for legal actions you took during the pendency of your lawsuit against HER, and her suit is for OTHER than malicious prosecution, your conduct may well have been privileged and she is maliciously suing you. You could in that situation, bring a SLAPP motion, which would promptly dismiss her lawsuit and entitle you to attorney's fees.

Two things are clear here: 1) you are caught up in a sue-sue-sue-sue cycle that may never end. Not a good thing. 2) Your situation is complicated and you have little hope of getting a meaningful answer on this forum. You need a couple of hours to sit down with a lawyer and let him fully understand the case and so you can ask all your questions. So do it.