Ariadne isn't a healer (though she does have first aid training) and likely hasn't gone camping in years, but she's tiny and looks vulnerable. If any Seelie come looking for them, she'd be a good choice to be all "oh no woe is me horrible things" etc. at them and distract them from the camp.

Also, she's learning to magically conceal herself, so she could be on watch -- the best guard is one you don't know is there!