Beth Harrison writes chick lit books set in DC -
https://www.goodreads.com/author/show/537929.Beth_Harbison
I've read 2 or 3 of them. They are mostly pretty light and fluffy, though there's a rape scene in one that comes out of the blue and is written really badly. That turned me off her books so I haven't read more but other than that they were easy beach reads.
Ellen Byerrum has a semi-cozy mystery series set in DC - under the overall grouping of Crimes of Fashion. These seem to be self published? Or I can't quite figure it out The DC library doesn't have many of them.
The Hopefuls by Jennifer Close was partially set in DC. It was good, centered around political ambitions and running for office.
Kathleen Gilles Seidel wrote A Most Common Degree of Popularity, set in the private school world of DC and upper NW.
I also seek out DC-based books - not as easy to find, and especially not easy to find chick lit or lighter things that aren't thrillers or all about politics.