First, hi neighbor. I used to live in Reston. I think you may need to rethink your approach and your thoughts on what is fair -- because you may end up on the short end of the stick on this. I applaud your patience so far, and in the interest of keeping your own sanity, I suggest the following:
Reframe the entire situation, and look at it as if you are maintaining a nice neighborhood. Maybe other neighbors will help out too.
1. why is it the husband's responsibility to provide maintenance and upkeep for the house? He's already paying the bills for wife to live there for free. I would think maintenance is a small price for her to pay to live in a lovely town like Reston.
2. If you were close friends with any neighbor, you would probably be over there helping with the house maintenance. So maybe just go over and help. You may get a wonderful friendship out of it and maybe she can repay you with a homemade meal once a week, or dog-walking, or gardening, or something else that she may have natural abilities for. Or maybe you'll just be teaching her how to put up siding and paint.
3. Consider this "your Detroit" and do whatever it takes (yes, your own time and your own money invested in order to keep your house above water) I know it's not fair, but then who ever promised life would be fair?
As an aside, my relatives live on a golf course that was recently bought by someone VERY rich and with a public personality. He purchased the home next door to my relative for his infrequent visits. He's rarely there, so he has no idea that his deck has wood rot or that the people he's paying to maintain his house aren't doing a good job. My relatives will be going to the nursery this weekend to purchase plants and they will plant them in HIS yard because otherwise, they have to look at his ugly-ass A/C unit. My relatives have done landscaping projects and have also cleaned off his deck because they're the ones who have to live with it. They've called the groundskeepers to let them know that his pipes were frozen, and they've picked up trash and decaying wood from his property and disposed of it properly. Sometimes I look at it and think "you should just call the news and let them know that this famous person is a derelict homeowner" and other times I think my relatives are just being neighborly. If this were the previous homeowner, whom they were friendly with, they would have done the same with no expectations of repayment, just because.
Sorry for the long response. Do what you can to remain sane. That's really what matters.