"Sweetheart of the Song Tra Bong" How does her gender change the reader expectation about her reaction to the war?

I'm not sure about other who've read the book, but my first reaction to Mary Anne's visit to the camp was disbelief and fear. The things men experienced in Vietnam were unlike any prior war.... I initially believe she'd turn around for home, or that she would be killed. The last thing I expected was for Mary Anne to bond with the men and join the cause.