She and her two sisters, Rose and Ada (died 1872), attended the exclusive Catholic convent school Gumley House for several years.

One of the most ambitious developments was an alpine garden, including a gorge and rockery, which Ellen's father gave her permission to create on her 21st birthday.

[4] Willmott received a substantial inheritance from her godmother, another keen gardener, Countess Helen Tasker of Middleton Hall, Brentwood, who died in 1888.

[1][2] Willmott inherited Warley Place on her father's death and continued to develop the gardens, indulging her passion for collecting and cultivating plants.

[1] Willmott used her wealth to fund plant-hunting expeditions to China and the Middle East,[1] and species discovered on these excursions would often be named after her.

[8] It has been claimed that she secretly sowed seeds of the giant prickly thistle Eryngium giganteum in other people's gardens, leading to it to be colloquially known as 'Miss Willmott's Ghost': this story first appeared in the 1980s and has been debunked, most recently in a 2022 book by Sandra Lawrence.

She also received the grande médaille Geoffroi St Hilaire from the Société d’acclimatation de France in 1912, and the Dean Hole medal from the Royal National Rose Society in 1914.

[4] This included 132 watercolours of roses painted by Alfred Parsons between 1890 and 1908, which are now held by the Lindley Library in London (Cory Bequest).

[3] In 1932, Willmott presented her Holtzapffel lathe, some examples of her ornamental turning work, and a number of photographs and slides of horticultural subjects to the History of Science Museum, Oxford.

[21] Willmott's prodigious spending during her lifetime caused financial difficulties in later life, forcing her to sell her French and Italian properties, and eventually her personal possessions.