Earthgrip — Harry Turtledove

Jennifer Logan was young, gorgeous, and utterly devoted to teaching Middle English. But to qualify for any decent teaching position, she'd have to make her resume stand out. Since her specialty was science fiction, she wrangled a berth on a trading ship bound for the stars. Just one trip, she figured, then back to a nice, safe classroom. . .

But Jennifer hadn't fully appreciated her own talent. She had a keen eye, a fresh perspective -- and all of science fiction to fall back on when the going got tough!