Along the lines of “Nifty Stuff That Ought to be in Romance Novels,” there are some famous women in World War One that would be fabulous sources for heroines.
I highly recommend Into the Breach: American Women Overseas in World War I if you’d like a good overview of the many non-combat roles women played in Europe during World War One. The book focuses on Americans, but I still think it’s a good starting point for general research, as it’s very readable and has an excellent bibliography.
Beginning in May of 1917, the Russian army had a battalion exclusively made up of women, commanded by Maria Bochkareva. About three hundred of the women were in combat; Bochkareva was wounded in the June Offensive.
Here’s another great book that focuses on military women: The First, the Few, the Forgotten: Navy and Marine Corps Women in World War I.
There’s a good Wikipedia page on Flora Sandes, a British woman who served with the Serbian army after becoming separated from her Red Cross ambulance unit, and was wounded by a grenade.
Hello Girls operated switchboards, often near the Front or under other dangerous conditions. Here’s more. They were finally granted the status of veterans in 1978, though not retroactively, meaning they did not receive benefits for the period when they were denied. Here’s another Hello Girl page.
Read more about women at the front.