It depends on the severity of the hoarding, and whether or not it's interfering with her life. Hoarding disorder is a very real psychiatric disorder. It used to be diagnosed as OCD, but now it's a separate disorder. However, it's not uncommon for hoarders to also meet the criteria for OCD.

But not everyone who hoards meets the criteria for the disorder. Some people just collect or accumulate a lot of junk, and then never get around to going through it and getting rid of some of it.

Hoarding disorder is an especially difficult disorder to treat successfully, and many (if not most) mental health professionals lack the expertise to treat it (and can sometimes do more harm than good if they go about it the wrong way - I've seen it happen). Ideally, someone with this disorder should work with a psychologist or psychiatrist who either specializes in treating it, or who at least has a lot of experience in treating it. Even then, treatment isn't always successful.

If her hoarding seems pretty serious, encouraging her to at least have an evaluation would be the place to start (if you have some clout with her, but don't expect her to be receptive to the idea). Many (if not most) hoarders don't seek treatment, and they tend to be defensive about and resistant to anyone getting in their "stuff" (even if they know their behavior is abnormal). They can be fiercely protective of the things they are hoarding, as they have a very strong emotional / psychological attachment to their stuff. And some feel ashamed or embarrassed and will avoid seeking help as a result.

If there's a safety issue (hoarding can be a fire hazard as well as a potential health hazard) then the authorities may need to be contacted to do a welfare check (especially if there are minors, elderly, or other vulnerable individuals living in the home, or if the person is hoarding animals).

I am not sure whether you can do much.

I have a similar situation with a relative who hoarded so much stuff in her apartment that she started sleeping in the streets (probably a 24hr McDonalds). We called the police who broke into her apartment. They were concerned that there was so many stuff that someone could be trapped in there. They got the fire services and environmental protection agency to take a look. Eventually, they cleared out most of the stuff.

When the relative found out about it, she was livid and refused to talk to us again. In fact, she disappeared completely. The police knew where she was but didn't tell us. They contacted a psychiatric hospital but they refused to take her in because they haven't seen her. This was not what we expected as there was clearly something wrong with her. But we can't help but to think that our intervention made things worse.

I don't know what the Government services are like in the US. But the fact is that she has her husband and children around and that might make them less likely to intervene.

Good stuff from Cali and Derek as usual, and what they posted do give you
forewarning about what might happen.

It seems like it's something you want to talk about with a local professional as
well as her husband. Husband first so he knows what might happen.

Maybe nothing you can do, and/or maybe it's not technically
hoarding. We don't know how much stuff and what kind of stuff
you're talking about.