In "Lyddie", Chapters 19-20, why did Lyddie work so hard after the farm had been sold?
Lyddie threw herself into her work when the farm was sold so she wouldn't have to feel so acutely the pain of what she had lost.
Lyddie felt like she had lost everything when the farm was sold despite her efforts to earn enough money to keep it. Because of her stubborn pride and consuming need for independence, she responded to Luke Stevens's loving offer of marriage with fury, completely misinterpreting his intentions by thinking he was doing it out of pity, or to own her. Her thought was that, with the farm gone, she "had nothing left but (herself), Lyddie Worthen", and so she defiantly and protectively shut herself off from anyone who might want to get close to her, and infringe upon her precious independence (Chapter 18).
The loss of the farm coincided with the departure of Lyddie's little sister Rachel. Lyddie experienced an intensity of loneliness after these two events which she had never known before - "loneliness was...this sharp pain in her breastbone dragging down into a dull, persistent heaviness". With "nothing to look forward to", she threw herself into her work, working hard "because work was all she knew, all she had...everything else that had made her know herself as Lyddie Worthen was gone...work alone remained". By working so hard, Lyddie found that she did not have time to think, or to feel. Her mind "became as calloused as her hands...she rell into bed exhausted and only felt the full burden of her grief in dreams" (Chapter 19).