Aku no Joou no Kiseki

Mari, a college student, wakes up and finds herself on a battlefield. Looking around in confusion, she sees many knights in Western-style armor, and they call out, “Her Majesty the Queen,” to her. Apparently, Mari’s “army” is in the midst of a battle, and they are badly outnumbered. Believing it to be a mere dream, she devises a plan to win the fight, but to her surprise…she is really in the body of a queen! In this miracle fantasy, an ordinary college girl struggles as a “queen” in a different world!

(Source: Alpha Manga)