She was an American citizen who moved to England at age 26. She made a second marriage to Waldorf Astor as a young woman in England. After he succeeded to the peerage and entered the House of Lords, she entered politics, in 1919 winning his former seat in Plymouth and becoming the first woman to sit as a Member of Parliament (MP) in the House of Commons. Her first husband was an American citizen, Robert Gould Shaw II, and they divorced. She served in Parliament as a member of the Conservative Party for Plymouth Sutton until 1945, when she was persuaded to step down.

was the first woman to sit as an mp in the uk house of commons an immigrant from the united states?
yes