The correct answers are She prefers walking to driving, She'd rather walk than drive, and She prefers to walk rather than drive.

With "prefer," we use the pattern "prefer A to B" (with gerunds) or "prefer to do A rather than do B." With "would rather," we always use "than" (not "to") to compare: "would rather A than B." Mixing up "to" and "than" between these structures is a very common mistake!