She was born into an evangelical Christian family in Kent, and after her father's death she increasingly campaigned against the use of plumage in hatmaking which had led to billions of birds being killed for their feathers.

She worked for many other organisations, including the Royal Earlswood Hospital, the Women's National Anti-Suffrage League, and the local Red Cross branch.

Etta and Mercy (the names that the sisters preferred to be called) initially lived with their father and stepmother at their new home in Blackheath, then a Kenitsh village ten km to the south-east of London.

[4] A major threat to birds from the late eighteenth century[a] up to just after the First World War was the demand for feathers to decorate women's hats.

Shooting breeding birds effectively led to the failure of their eggs and chicks to survive, causing actual losses to be much higher.

[6] Smith was inspired by Scottish naturalist Eliza Brightwen's Wild Nature Won by Kindness (1890) on the killing of birds for the plume trade.

[11] The amalgamation was brokered by the Royal Society for the Prevention of Cruelty to Animals (RSPCA) which did not itself wish to take up the plumage cause; as a moderate mainstream organisation, it was politic for it to keep some distance from what was seen as an extremist movement.

[19] She was as Mistress of the Robes to Queen Alexandra,[20] consort of Edward VII, and her Duke was Master of the Horse, both roles that placed the couple close to the monarchy.

[24] In July 1919, Lemon and the Duchess of Portland delivered a letter signed by 150 men, including celebrities such as H. G. Wells and Thomas Hardy, to the president of the Board of Trade, Sir Auckland Geddes, asking that the war-time restriction on the importation of plumage should be continued until legislation was passed.

[27] When the secretary of the RSPB, Linda Gardiner, retired in 1935, there was a proposal to replace her with a man, apparently to give the society greater acceptability.

[2][28] Lemon soon came under scrutiny in The Field where an editorial in 1936 questioned the Society's inaction on cage birds, its gambling on real estate investment, its high expenditure, and its elderly management.

This led to the establishment of a six-member committee headed by Julian Huxley of the Zoological Society of London that proposed changes in the management which included fixed terms for elected members.

The post of honorary secretary had been abolished, and practices she disapproved of, such as bird ringing and close photography, had been adopted by the RSPB, whereas she felt that her watchers were undervalued.

An 1896 SPB pamphlet A Woman's Question written by Blanche Atkinson and distributed by Lemon noted that the wearing of plumes by women was a good reason to deny the right to vote: "if women are so empty-headed and stupid that they cannot be made to understand the cruelty of which they are guilty in that matter, they certainly prove themselves to be unfit to be voters, and to enter the learned professions on equal terms with men.

[6][32] Lemon also worked with the Royal Earlswood Hospital in Redhill, Surrey, one of the first establishments to cater specifically for people with developmental disabilities,[33] and the Crescent House Convalescent Home, Brighton.

[2][34] In 1911, Frank Lemon became mayor of Reigate, and as lady mayoress, Etta became involved in his civic duties,[35] including organising a Christmas party for 100 children.

[2][29][f] Lemon was one of the first four female honorary members of the British Ornithologists' Union (BOU), admitted in 1909;[39] the others were the Duchess of Bedford, Dorothea Bate and Emma Turner.

She saw professional ornithologists as largely unsupportive of her cause, and since much BOU activity at the time involved egg-collecting and killing birds for study and for their skins, she saw them as part of the problem she was trying to solve.

[2][40] Lemon's selflessness won her the admiration of many, particularly her watchers and the soldiers from the war hospital,[41] but her conservatism and authoritarian methods earned her the nickname of "The Dragon" at the RSPB.

[43] In 2021, Nature's Home, the RSPB magazine, published an article commemorating the women who founded the society, Lemon, Williamson, Phillips and Winifred Portland.