Welcome, Dorothy!
Always nice to hear someone else is working to understand the difficult folks we all come in contact with!
Several thoughts: For support for you, consider contacting Vick Kelly (see the Tomkins Institute home page for address),and finding out if there is a Tomkins study group in your area. It is incredibly helpful to have colleagues to help wrestle with affect theory. If there is no study group, Vick can help you get one started. I, and many others in the Institute would be happy to offer moral support.
I suspect that the difficult family member is operating in the attack-other script library of Nathanson's compass of shame. I'm not clear on what is triggering shame for this person. You may very well be right that early wounding (abuse or neglect) has contributed to a personality style where this pattern is prominent. It was interesting that the daughter didn't even think her siblings were doing a good enough job taking care of Mom. (I recently had a new patient who complained angrily about other physicians. As I got to know him, I suspected it wouldn't be long before he was angry at me. It wasn't.)
I don't have any magic answers for working with these folks. We certainly can take care to interact in a compassionate and non-shaming way, which I suspect you've been doing. Even in therapy, it is a tough pattern to change---when they realize they have a problem. One of the things that helps me in working in therapy with traumatized people where attack is prominent is to realize how much real shame and often distress or fear is behind the attack, and it helps me not to take it personally. In some patients the attack can melt into tears or fear very quickly. The attacks may have been how some of my patients survived in fimilies that felt like a continuous nightmare. Maybe that can help your staff, although we don't know alot about this woman's background. Setting firm limits (on their abusive behavior) can be tough in these cases, too!
I hope some of our colleagues can help further.