TS Eiseihei-san no Senjou Nikki

As someone "blessed" with the rare potential for recovery magic, Tory Noelle is drafted as a combat medic at the tender age of fifteen. Fighting as a teen soldier won't shake her confidence, though—not when she can recall carefree days of playing first-person-shooter games in a previous life. But a world full of magic isn't as fun as it once seemed. Now living the nightmare that was once her playground, Tory faces a serious question: can she build her skills fast enough to buffer against the brutality of war, or is she doomed to become another bloody stain on the battlefield?

(Source: J-Novel Club)