[1] Born in London as Sicele Julia Mary Annette O'Brien to Sir Timothy Carew O'Brien, 3rd Baronet and Gundrede Annette Teresa de Trafford, daughter of Sir Humphrey de Trafford, 2nd Baronet of Lancashire.

Her father was an England and Ireland cricket captain and Deputy Lieutenant as well as Justice of the Peace for County Cork.

[4] Her father also served and her older brother Timothy was killed in action in Flanders in 1916.

[5][page needed][6][1] With Mary, Lady Heath she set the 1928 British Altitude record.

[7] On 20 October 1928 she lost a leg in a flying accident near Mill Hill golf course Middlesex while giving training in her de Havilland Moth.