It is the fourth book in The Diabolus Chronicles (Pitch & Sickle series).
For public domain classics that contain the term "greensward," you can explore the Project Gutenberg EPUB Library. Download The Greensward Girl epub
by Emilia Hart: A novel following three generations of women with a deep, magical connection to nature. It is the fourth book in The Diabolus
You can find digital and physical versions on Amazon and ThriftBooks . Similar Titles You Might Mean the "Lady's Horsemen
If The Greensward is not the correct book, you may be thinking of one of these similar "Green" themed titles:
The story follows Silas and Pitch, the "Lady's Horsemen," as they investigate a tortured spirit in Devon. The narrative explores themes of forbidden magic, necromancy, and the evolving attraction between a human and a daemon.