No, Harriet Beecher Stowe did not directly work to improve conditions for the mentally ill. Stowe is well-known for her writing and activism against slavery, particularly through her influential novel "Uncle Tom's Cabin." While she was empathetic towards the plight of oppressed individuals, including slaves, there is no significant record of her involvement in advocating for better conditions or treatment for the mentally ill. Her focus was primarily on issues related to slavery and women's rights.
