In June 1915, Henderson became honorary secretary of the Scottish Women's Hospitals for Foreign Service and her fundraising effort took place in large and small venues, encouraging organisations to raise funds or to sponsor named beds e.g.'''Broughty Ferry St. Margaret's School Bed',
and the Montrose Girls Club Bed'' (at SWH
Royaumont, France). Having returned from visiting SWH units in France, Henderson gave lantern talks and presided over an entertainment for the wives and children of the active service troops. Another large audience heard from Henderson as to why these 'brave women' were treating Allies and not their own wounded (because the British Army and Red Cross had told Dr. Elsie Inglis that the women were not needed), but the women's hospital services were welcomed by the Belgian, French and Serbian Allies. She reported that the SWH operation had grown to 250 staff covering 1,000 beds. Henderson remarked that the French
General Joffre had donated 300 of the 1000 francs given for French hospitals to the SWH.
Dundonians had raised £1,500 and local people were at SWH; Dundee university graduates: Dr
Laura Sandeman, Dr Lena Campbell in Serbia and Dr Keith Proctor in France; Miss Shepherd and ex-Provost Lindsay of Broughty Ferry's daughter. Later that year Henderson spoke in
Brechin, and at the local suffrage society in
Cupar, who sponsored a
Cupar-Fife bed (in SWH Serbia); Dr. Inglis was herself a Scottish suffragist. In March 1916, Henderson presented 'the grand mission' of SWH at a well attended local fund-raising concert, and chaired an event with Dr
Alice Hutchison speaking on the SWH in Serbia (in the place of Dr Inglis in April 1916). The news of her departure to join Dr Inglis herself, was said to have 'disturbed' the 'wonted even tenor' of the DWWREC, as they would miss her dedicated service, but there was public recognition in the city and in national suffrage societies that her skills would be of benefit to Dr Inglis's unit.
Role as administrator in the Serbian SWH Unit Henderson then served as an administrator in Serbia The Unit set sail from Liverpool on 30 August 1916, and Henderson sent a postcard saying 'all well' on 21 October 1916. In November 1916, Henderson had sent a postcard from
Odessa. Henderson had left the group with a small team to find Dr Chesney's unit but the women got separated from the Serbian forces, sleeping in the open air, before reaching 'civilization' with the Russian authorities, at
Reni. Then they travelled by rail with Dr Inglis group although she said with overcrowding on the train, she saw a Russian doctor prevent a soldier with cholera from boarding, which she said was the most 'pathetic' thing she had seen in her experiences, 'that poor man put off the train and left in the darkness'. The train was also almost bombed by enemy aircraft, but for the quick-thinking of the train driver. Challenges arose in crossing occupied country, and Henderson remarked that, despite the group being in mortal danger, very little equipment was lost. The next tent hospital at Boulboulja was exposed to enemy aircraft by sitting on a wide plain. Again the women in the transport teams worked as soon as they had 'scarcely arrived' to bring in the wounded for urgent treatment, despite their lack of sleep. Henderson's stories about the Serbian (Rumanian) retreat were featured in ''
The People's Journal'' and she said that in grey khaki uniforms, and with a military demeanour it was 'almost impossible' for local 'peasants.. at first glance to guess their sex.' She said Serbians and Rumanians 'knew' the people from the Scottish Women's Hospital as 'angels in disguise'. She was back home to organise equipment supplies following the retreat, travelling via Norway. In November 1917, Henderson gave another lecture in Dundee and 'held the attention of a large audience' with her 'power of description' and images of the work of the hospitals, and she emphasised the importance of the allies in Belgium, Serbia and Rumania to the overall war effort. She said that of 60,000 boys (over 11 years old) who had left during the Serbian retreat, only 15,000 had survived. 45,000 had died on the road, or later from exposure. She then spoke in Manchester, in July 1917, in aid of the
Rumanian Red Cross.
Writing about the war Henderson wrote about her experiences, as some other women in the SWH did, in war diaries and she wrote poetry. one critic described it as ' worthy of
Kipling at his best'. In another poem,
The Incident (probably a culmination of many such incidents she witnessed), and his nurse to a mother or the Virgin Mary and she composed to a similar theme in ''A Young Serbian'.'' In another poem she dedicated 'to the rank and file of the Elsie Inglis Unit', titled
Like That, based on a quote from the Prefect of Constanza:
No wonder Britain is so great if her women are like that , Henderson writes of the war nurses as being as heroic as the men under fire, == Post-war Women Citizens Association ==