Ghosts of 1914 has a fun post about dressing up as a WWI nurse for Halloween, with a link to the National Library of Scotland’s photos of women who actually served on the Front, rather than behind the lines.
http://ghostsof1914.blogspot.com/2012/10/what-to-wear-to-war-halloween.html
Fiona also has a link to her past posts about period costumes.
And for the real thing:
http://camc.wordpress.com/2012/03/09/ww1-canadian-nursing-sister-uniform-part-1-service-dress/