Viscountess Rhondda, a hereditary woman peer in her own right, was the first woman to petition to take her seat in the House of Lords. No woman had attempted this previously because of long-established custom and lack of precedent. Although her petition was ultimately refused by the Committee for Privileges in 1922, it was a legal landmark in establishing that legislation was required for women to enter the upper House of Parliament and an essential stepping-stone in the process which eventually led to women entering the House of Lords as life peers in 1958, hereditary peers in 1963, and bishops in 2015.
The full version of this landmark is written by Mari Takayanagi