Q. My daughter-in-law hates me and has said vile things to me. She thinks I’m evil, and she’s stolen my son from me. When they first started dating, she adored my son and was very good to me. After they got married, she somehow decided I was the enemy. Now she won’t let me see my son or even talk to him on the phone. She berates him all the time, and I’ve learned she threatened to kill herself if he tries to leave her. She is so angry that I can imagine her going crazy sometime and hurting him. What on earth can I do?

A. From your description, it sounds like your daughter-in-law may be suffering from severe mental illness. While it could be several different conditions, you are describing many of the symptoms of Borderline Personality Disorder (BPD). One BPD symptom involves viewing people in black and white, either all good or all bad. Often, someone who suffers from BPD can start by idolizing someone. Then, after they are (inevitably) let down in some way, they view the other person as bad, dangerous or even evil.

One of the most painful things for a person with BPD is that they can’t manage their emotions. Their moods swing wildly back and forth. They often feel desperate, like an abandoned child. In order to keep people from leaving them (or even from setting healthy boundaries with them about their behavior), they will make threats — like killing themselves.

BPD can be effectively treated, usually through a combination of individual and group therapy. The most effective approach is called Dialectical Behavior Therapy (DBT), and it teaches patients to manage their emotions and their relationships. Your daughter-in-law would have to be willing to get help. This may not happen unless someone — your son most likely — is willing to take a strong stand and stop complying with her dysfunctional behavior.

Try to find some way to talk to him directly. Can you deliver a message to him through a buddy of his or contact him at his place of work? Don’t create a web of secrets with him; just have a plain talk about your concerns and learn if he is willing to take action.

Hopefully, something productive can be done, but it may also be that your daughter-in-law is too abusive for the situation to be salvaged. If you are worried that your son is in immediate danger, you can call 911. But I would be extremely careful about taking this step — because if the cops don’t find domestic violence occurring at the time they visit, this will only escalate her hatred and mistrust of you, and possibly her abuse. She might also be able to manipulate the situation to cause your son to be arrested.

Please do everything you can to take care of yourself. Consider consulting with a mental health professional or an expert on domestic violence to figure out how best to respond to this situation. If you fear she might act out against you directly, you can request a temporary restraining order from the courts to protect yourself. And be sure to get plenty of support from your friends and family.