It sounds like you can get her to accept a "time out" if you catch one of her rages in its formative stage. Once the fire builds up to an epic level, she is no longer open to "taking a break" and will even follow the person she is raging at.
As far as that goes, work around it if you can. Perhaps you and husband should both leave for an hour to go shopping, if she will at least refrain from following you into the car.
Next, catch her sometime when she is very calm, and explain that all three of you need to take a break when she cycles into a rage. See if you can get her to make a commitment to let the time out take place, to promise not to follow you around. If she can willingly make that commitment when she's in a calm state, then when she cycles into a rage she'll at least know in her mind that she did make a promise.
Finally, catch her as early as possible in her rage cycles. Try to catch her before it becomes an actual "rage." If she's just beginning to get unreasonable, tell her immediately that "This isn't going to be a good time to talk; let's all cool off and take a break. We'll talk again in about an hour." If you can catch her soon enough, before she cycles too far into the rage, she may still be able to reason enough to agree to "taking a break."
I think it will help if you can find ways to suggest taking a break without "singling her out" (even if she is ground zero). Look for phrases more along the lines of, "We're all getting a little testy here; let's take a rain check and talk again after we've all cooled off." I know that might sound like coddling her if she's the only one that needs to cool off, but you have to keep in mind that when she is in a rage state, she will interpret virtually everything as an attack against her as a person. And then of course she'll "have" to defend herself. So try to use statements that diffuse the appearance of a spotlight being on her. Let it "be" all three of you that needs to calm down. If she can swallow that pill, then the diplomatic sugar coating might be worth it.
It seems obvious enough that she is ashamed about her condition. That shame will morph into defensiveness when she goes into a tantrum. When she is angry, she won't want to be vulnerable. So then she'll start defending her faults. So when she goes into a tantrum, look for any little way to help diffuse her "need" for defensiveness. Try to remind her that the three of you constitute a team, that you all have your faults, and that you're all working together to try to help each other do better and get everyone's needs met.
These ideas and principles won't always suffice. She'll still often freak out so badly that she becomes quite impossible to manage. But if using these ideas and principles helps stave off even one or two of her would-be rages, then we've made some progress.
The biggest thing to keep in mind, I suppose, is that she can be reasoned with when she's calm; she can't be reasoned with when she's angry. That means that each of her calm states is an opportunity to negotiate with her to make commitments about what she'll agree to do during the rage states that are to come. When she's angry, all you have to work with is whatever foundation you were able to lay when she was calm. So take advantage of her calm states; they are golden opportunities.
And brace yourself for the chaos when she loses her cool, because there will be chaos. The first ten times you try to get her to "keep a commitment about taking a break," she may shout, "Screw your stupid commitment!" and continue to follow you around. But when she does calm down again, you sit down with her and ask her to confirm that yes, she should have kept the commitment she made. Maybe after the tenth tantrum, there will finally be one tantrum where she keeps her word (and lets everybody take a break). That's precious little progress, but progress nonetheless. It is (I believe) the beginning of a later stage in her life where she will hold to her commitment nine times out of ten (instead of just one out of ten).
Yah, it will probably take years to really chip away at these problems sufficient to be able to look back and say, "We really have come a long way," and, "We really are happier now."
It's all about figuring out little ways to mitigate the rages. With enough tinkering, the work may reach a point of critical mass and she may actually have a visible break-through. We can always hope, while stubbornly struggling along and doing the tedious work.
I am convinced that if she (with your help) can find healthier ways to cope with her angry feelings, then the chasm between her and your husband will start to close. The long-needed apologies will start to flow. And maybe, just maybe, your husband will start to feel like there's hope for him and her again.
Love means never having to say, "Put down that meat cleaver!"