Dream-Shifter by Lois Wickstrom

Middle school student Gwendolyn is a dream-shifter. This means that when she dreams, she becomes what she dreams about, and she dreams about being different animals. If she awakens naturally, she becomes a girl again. But a fire alarm jars her awake when she’s dreaming that she’s an elk. She awakes as an elk. It’s elk hunting season, and she doesn’t know how to change back to a girl, or how to stay alive.