Q. My sister, 45, has three daughters, ages 17, 16 and 6, a sharp tongue and an ex-husband who has remarried and started a new family. He is barely involved with his girls, however, although he does send a child support check to my sister every month.

The children’s basic needs are met, and there is no physical or substance abuse in the home, but these girls have lived on the edge of an active volcano ever since their parents got divorced five years ago. Somehow, my sister’s temper has gone from sharp to nuclear. And when I say nuclear, I mean that she explodes like Mount St. Helens! She uses tough (but acceptable) language when she talks to her daughters in public, but her outbursts at home are extraordinary. Although these eruptions only occur every one to two months and are only directed at her daughters, the girls still seethe with resentment, scream back in self-defense, slam doors and storm out of the house in tears.

Here’s a good example: When one daughter accidentally broke a mirror, my sister screamed at her until her voice was hoarse, her face was purple, the veins in her neck were bulging, and she was doubled over and pounding her fists on her thighs. If I hadn’t witnessed this fury myself, I would never have believed it. Within a few hours, however, she cooled off and acted as if nothing had happened.

I’ve tried to talk to my sister about these angry explosions, but she clams up and says she can’t help it. I know that she is strapped financially and is still furious because her husband left her for “greener pastures,” but I don’t think she should rest her rage on the skinny shoulders of her young girls, especially when there is no adult to intervene on their behalf.

The two older daughters can’t wait to leave home, but they’re afraid that their little sister won’t be able to fend for herself. My heart breaks for her, too. And yet somehow, these girls do well in school, have a lot of nice friends and don’t get into scrapes.

I can’t help my sad sister much since I live 300 miles away, and I can’t give her much money since I have my own family to raise, but is there anything else that I can do for her and my wounded nieces?

A. You have a double problem: your sister and her girls — and the girls take precedence. The needs of children always come first.

You can Skype with the children every week — if they’ve got a computer — and write to them when you can whether they have a computer or not. Letters delight the young, especially when you tuck a cartoon in the envelope, so they’ll have something to laugh about, or a few dollars, so they’ll have a little walking around money. And please, invite your nieces to visit you for a week, one child at a time, as long as they live at home. When these youngsters are with your family, they will be swapping their pain for a little peace and giving your sister a small respite too — and all for the price of three round-trip bus tickets a year.

You can help your sister, too, and it shouldn’t cost much. She may ask you for money occasionally but she needs your love a whole lot more. She needs to know that you care.

Treat her to an occasional manicure, just for fun, and call her often, just to let her vent. Don’t tell her what you think she should do, however, because she has probably had too much advice already.

That’s not all this family needs, however, as divorce can hurt more than death itself.

To help your sister and her children get through this dark passage, try calling the mayor’s office, United Way and some churches and temples in their town to see if they know of a grief counselor who conducts free — or almost free — meetings for the tentacles of divorce can be toxic. If it arrests the children’s development, it could cause them to react to the stressors of life as if they were no older than they were when the divorce took place and it could keep your sister as angry as she is right now — or even angrier. Behavior is often magnified as we get older.

You can help your sister move on by sending her a copy of “Divorce Hangover” by Anne Newton Walther, M. S. (Tapestries; $15). It won’t make her hangover go away, but it may make her treat her girls more kindly.

Questions? Send them to advice@margueritekelly.com.