Dahlgren's estate was on South Mountain, Maryland, overlooking the battlefield. In 1870 and 1873, she actively opposed the movement for female suffrage, and drew up a petition to Congress, which was extensively signed, asking that the right to vote should not be extended to women. The Literary Society of Washington, of which she was one of the founders, held its meetings in her house for six years, and she was elected its vice-president. She was for some time president of the Ladies' Catholic Missionary Society of Washington, and built the chapel of St. Joseph's of the Sacred Heart of Jesus, on South Mountain.