I don’t personally think that you should sue. I tried pursuing a lawsuit against a former therapist of mine, and many lawyers acknowledged to me that what she did was very likely illegal, but the evidence is largely hearsay and those cases can very rarely be won by the client.
What I ended up doing with my ex-T was reporting her to the Office of Professional Discipline, and they are taking my claim seriously and investigating it. Will I get any monetary compensation out of it? No. But, I can make sure I’m doing my part to protect her future clients from similar misconduct, as she can be subjected to disciplinary action, if found guilty of misconduct. So, at least she might be held accountable for her actions. If where you live has something like that, it might be worth looking into.