One of my experiences with an entire lot purchase was from an older guy in his 80s selling his walnut hoard. As i was loading it up, he talked to me for awhile and he commented at one point, "i have to get rid of this while im alive for fear my wife desecrates my body". Made me chuckle as i was loading the boards. He made a fair point.
A few years back I got about $1K in rough walnut, cherry and a few other choice pieces from the estate of one of my neighbors for free. They didn't know what else to do with it, figured I'd use it, and sorta "owed" me for fixing our shared fence, which cost around $1K. (They've got dogs, we don't, and don't need the fence.)
I was given hundreds of BF of teak from a friend's estate which had been sitting around since the '60s. There was also white oak which was about half rotted, but I was able to cut away the bad parts and save a lot. There was some powderpost in the basement where the wood was stored, but none in the wood I took. About 1 1/2 years ago.
What about looking for an enterprising H.S. or college student to sort and sell for a 50% split?
Did the neighbor give you any idea what she thinks it is worth or what she would be willing to sell it for?
Over the years I have helped some people sell off tools and antique firearms. More often than not they think what they have is worth a king's ransom when it was not worth much. I wish you the best.
A couple of FB groups may be useful. There is 'Virginia Woodworking and Maker Buy and Sell' if you want to try listing there, and 'NOVA Woodworking Community' if you want to put the query out to local folks. Presumably similar group(s) focusing on the other side of the river.
Sometimes the easiest solution is a tax deductible donation to a charitable organization that will haul it away and is accustomed to dealing with anything and everything. In my area we have a few that take building supplies and salvage from demo projects. People like Habitat for Humanity come to mind also.
The fact that this material was stored in the dirt is a big concern. Dirty wood will play hell on planer knives, blades and cutters. Outfits that deal in salvage or reclaimed material don't care about that as much.
In response to some of these Qs--I don't think this woman is looking to make a killing on this, she mostly wants to put it all in good hands and not get completely ripped off. The advice to go to Facebook is a good one.
Another option would be a donation to the local high school construction trades or shop class. The donation could be in her husbands name, and it would be helping youth looking to be working with wood projects or jobs.
I'm in the DC area and would be interested in taking some of that wood off her hands!