One of Leonard's top ten female villains, as shared at the Guardian:
Miss Slighcarp in The Wolves of Willoughby Chase by Joan AikenRead about the other entries on the list.
Letitia Slighcarp is a greedy con-artist after Sir Willoughby’s money. She takes control of the house, fires the staff, dresses in Bonnie’s mother’s rich clothes, and goes through Sir Willoughby’s papers. She treats the girls appallingly and when they get in the way of her schemes she sends them off to a workhouse as orphans. Slighcarp is an A grade criminal.
Also see Emerald Fennell's top ten villainesses in literature.