The only serving female casualty of the French Flag Nursing Corps seems to be Clementina Addison. I have not come across Marie De L'Epine and, as Sue has mentioned, had probably resigned pre-death.
There are two other casualties that had served with the FFNC but had moved on prior to their deaths.
Ella Kate COOKE, QAIMNS had been a member for eight months.
Lily LIND, New Zealand Army Nursing Corps was in the FFNS in October 1914.
Alice WELFORD, QAIMNS, was one of 16 nurses from St.Bartholomews Hospital who was sent to France under the French Flag Nursing Corps in November 1914..
Thanks for the information. The lit I was looking at had the dates the nurses served in the FFNC and Marie De L'Epine was down as leaving June 1917 with a note deceased. Whilst I thought this meant she died then it seems obvious that dhe just left and as you report she died in 1918. What nationality was she and where did she die?