Wife verbally abuses husband’s family

Dear Carolyn: My wife occasionally picks fights with members of my family of origin, especially my sister. What am I supposed to do about that? The general guidance is that protecting my spouse from my family of origin is my responsibility — they’re my family, not hers — but it was my wife that started the whole mess.
My mother died last year; she was cremated. Her ashes are in a box on my sister’s mantle. She will eventually be buried with my father, but he’s in a National Cemetery and there’s a long lead time before that can happen.
When we visited my sister, my wife went on at length about how my sister is disrespecting our mother by having her ashes in a plain wooden box on the mantel, rather than in some fancy urn. Sister did not take wife’s opinions well. She’s furious. Wife is demanding I step in and defend her. My selfish view is, you started this, it’s on you to finish it. What should I be doing? — Anonymous

Answer: Agh! Yes your “You started this, it’s on you to finish it” view is selfish. Please reconsider. Immediately.
You’re halfway to doing the right thing in not defending your wife for her awful — awful — remark about the ashes.
The other half you need to cover is the reverse of your “general guidance”: You need to protect your family of origin from your wife. Preferably in the moment, not after the fact. Wow. If I could, I’d demand that you “step in and defend” your sister, with your wife in the room.
So. How’s your marriage otherwise? Is your wife as abusive to you as she is to your family? “Taking a hard look at the person you married” is the most important answer to your “What should I be doing?” question. People who think it’s their place to dish out unsolicited criticisms “at length” and to demand loyalty when challenged are rarely healthy themselves, and they’re almost never pleasant companions. Don’t fall in line with miserable expectations just because you got the idea somewhere that it’s what marriage is “supposed to” mean.
If what you describe as “occasionally picks fights” is just a nice way of saying that you are routinely in the position of having to clean up a mess your wife made with people you care about —wheck, even if it just has happened enough that it’s all familiar to you — then it’s time to ask yourself whether it’s healthy to stay in this marriage. A good therapist can help you answer this question, or ask it, in case you’re not ready to. Go alone, though; couple’s counseling with someone abusive merely opens a new front for the abuse.