The Lord’s Persuasion of Lady Lydia by Raven McAllan

Dang when Lydia is out for blood it's up to Harry to settle her down:
                 ‘Lydia, my love, you did promise to curb your bloodthirsty tendencies,’ Harry said with a laugh.
                Lydia scowled. ‘Damn, so I did.’
I really liked this book, Lydia knew how to give Harry hell.