There are some aspects of your post which bother me. In particular:
"Her manner with me was unsupportable; I made an agreement which kept her
free from annoyance, and she will not honor her part."
There was a "request", but not really an "agreement"; and she owes no
one
anything, nor do we have any right to expect any consideration from her.
In approaching her, I think that the view that must be taken has to be based
on:
1. This was Don's legacy
2. This was what Don would have wanted
I think that any other approach is likely to come off as self-serving, and
is unlikely to produce any positive outcome.
I also think that "deluging her with requests" is likely to "piss her
off",
and risk creating a situation in which she says, ultimately, "I called a
trash collector and had it all hauled away so that none of you would have
any further reason to contact me about this".
I don't feel that there is any way of getting through to her other than by a
close personal friend. I don't think that anyone who she doesn't know
personally is likely to be able to induce her to take any action whatsoever.