The following Archive might lead you to more information and might be willing to forward a letter to a family member. There are contact details for the archive including an email address.
"Ludmila Mlada/Ludi Horenstein Archive: Scrapbooks, photographs, music scores,
and vinyl records of an English dancer who danced with the Ballets Jooss and studied
with Sigurd Leeder. Accession listing available to view at the NRCD."
Also there was an obituary in The Dancing Times:
Obituary: Ludmila Mlada, Sheila McCarthy, Ronald Emblem
The Dancing Times, 2004, vol. 94, no. 1122, pg. 67
Thanks for your help, will try Dancing times first.