Cust, Aleen Isabel (1868–1937), veterinary surgeon and first female member of the RCVS, was born 7 February 1868 at Cordangan Manor, Co. Tipperary, elder daughter and fourth among six children of Sir Leopold Cust (1832–78), land agent to Mr Arthur H. Smith-Barry (qv) (later Lord Barrymore), and Charlotte Sobieske Isabel Cust (1835–1914), daughter of Vice-adm. the Hon. Charles Orlando Bridgeman. The family moved to England on her father's death in March 1878. Her paternal grandfather was Sir Edward Cust (1794–1878), army officer, historian, and politician. Educated privately, she initially began training as a nurse before turning to veterinary medicine. Financing herself from a number of modest bequests, she moved to Edinburgh in 1894 to prepare for the matriculation examinations that were a prerequisite to entry into this discipline. Ostracised by her family, who did not approve of her proposed studies, she endured great hardship. In 1896 she was admitted (under the name ‘A. I. Custance’) to the New Veterinary College, Edinburgh, which had been founded by Professor William Williams in 1873.
Although Cust successfully completed her studies in 1900 at the top of her class, she was not permitted to sit the examinations of the RCVS due to her gender. As a result she was unable to obtain the RCVS diploma required to practise as a veterinary surgeon. Highly thought of by Williams, with a testament from him she secured a post as assistant to William Byrne, MRCVS (d. 17 April 1910), of Roscommon. Byrne had qualified the year previously at the Royal Veterinary College, London, and inherited Castlegrange, Athleague, Roscommon, where he established a veterinary practice. Quickly fostering a reputation as an excellent vet, Cust later established a practice of her own at Ballygar and later again at Athleague. She also held three veterinary dispensaries. A prominent visitor to the veterinary congresses in Dublin, she attended the 8th International Veterinary Congress at Budapest in 1905. When Cust was appointed veterinary inspector by Galway county council (1905) attempts were made to have her removed because she was not a practising member of the RCVS, but she managed to retain the post nonetheless.
On the outbreak of the first world war she joined the remount department, and in 1915 went to France to work with the YMCA. She later enlisted in the Queen Mary's Army Auxiliary Corps, where she worked as a bacteriologist with an animal vaccine unit (January–November 1918). Nearly dying of pneumonia in France, she convalesced in England before returning to Ireland to pick up the threads of her practice. During the Troubles of 1919–21 her house was attacked by the IRA and her car appropriated. Following the passing of the Sex Disqualification (Removal) Act (1919) Cust was accepted as a candidate for the final-year RCVS exam. Owing to her war service she was required only to sit the oral examination and graduated 21 December 1922, the first woman to be awarded the diploma of membership of the RCVS. In 1924 she moved to the New Forest, Hampshire.
A good shot and a bold rider to hounds, she was a plucky and warm-hearted person with an impish sense of humour. She never married but in 1904 had been engaged to Bertram Widdrington, son of her guardian. It is also said that she and William Byrne lived together as man and wife. Her brother was Capt. (retd 1918) Sir Charles Cust, RN (27 February 1864–19 January 1931), equerry (1892–1918) to King George V. Unreconciled with her family, she died 29 January 1937 in Kingston, Jamaica, where she was on holiday. Her estate was valued at £29,915, which was bequeathed to the RCVS for the foundation of a scholarship.