Good friends of my mom's who have somewhat limited means have been very happy in independent living at Asbury Methodist Village in Gaithersburg and at Friends House Sandy Spring. Both far enough out to suit the non-urban resident and within a reasonable drive, though not a commute I'd want to do every day. I haven't visited Friends House myself but Asbury has a lovely campus with lots of green space to walk.
You definitely want to look for a continuing care community so they don't have to move to a whole different institution if their needs increase.
Nonprofits would be good, which both of those are.
In both cases, the friends who like those places are retired teachers, in one case from a lower cost of living area so they didn't have a DMV-level-appreciated house to sell. I don't have details on the finances, but I know it has been possible for them, which is encouraging.
I have also heard very good things about Collington in PG County, which is affiliated with the Kendal group, a really excellent group of nonprofit continuing care places. Here's their website:
https://collington.kendal.org/ . A friend's mom is about to move in but hasn't yet, so I don't have a first-hand report.