Bridge. On the floor or on the a stability ball. If you she feels nothing after 1 set of 12-15 reps add weight. Put a plate, medicine ball, dumbell on her lower stomach. This will hit the glutes something great! Number 2. Dumbell squat. Set up legs out wide. Hold single dumbell between your legs in front of you. Drop glutes doward floor till your near seated position and rise back up. Hits inner thighs and quads to but is a great glute exercise. Wide deadlifts as well. Gotta get those calves out of the movement.
PS. Her legs are gonna get bigger no matter what she does. The bridge however is the best option.