The Hon Louisa Lelias Plunket was born on 7 November 1833, the daughter of John Span Plunket, 3rd Baron Plunket of Newton (1793-1871) and Charlotte Bushe, daughter of the Right Hon. Charles Kendal Bushe, Lord Chief of the Court of King's Bench in Ireland. Her siblings were: william Conyngham Plunket, 4th Baron Plunket and Archbishop of Dublin; Charles Bushe Plunket (1830-1880); David Robert Plunket, 1st Baron Rathmore; Hon. Arthur Cecil Crampton Plunket (1845-1884); Patrick Henry Coghill Plunket (b. 1845); Anna Plunket (d. 1884); Katherine Frances Coghill (d. 1881); Hon. Charlotte Plunket (d. 1878); Emily Mary Plunket; Selina Maria Plunket; Josephine Alice Plunket; Isabella Katherine Plunket.