Newmark401 has the major merit of these discoveries
They had also another sister, Suzanne, but I don't know if she played too.
https://genealogie.deprelledelaniepp...d=prellenieppe
CHRISTINE CHARLOTTE ELISE GHISLAINE de PRELLE de la NIEPPE
Belgium
Born 11 June 1889
Died 8 November 1978
Married Louis Georges Raphael Rigano (3.1.1887-20.7.1962), 5 April 1921
RU: 1913 Bad Ragaz
MADELEINE GERMAINE AUGUSTA GHISLAINE de PRELLE de la NIEPPE
Belgium / Netherlands
Born 5 February 1893
Died 4 June 1960
Married Ewout Prins van Westdorpe (1.11.1879-14.6.1950), 10 November 1926
Winner: 1923 Swiss Championships, 1935 Château-d'Oex
A Mme de Prelle won in Gstaad in 1925, but I don't know her identity.
A photo of Madeleine
Source:
http://www.tennisforum.com/59-blast-past/497938-blast-encyclopedia-female-tennis-players-247.html#post69753881