Put her favorite food treats on some of the platforms. Rub the post down with catnip. Most cats scratch immediately after waking while performing stretching exercises. As soon as your cat wakes up from a nap, call her to her post. Scratch the post at a point a couple of feet off the ground.
Most cats reach up and stretch with their front paws on the post.
Praise your cat profusely, especially if she makes scratching motions. Don't try to physically force your cat to scratch by holding her paws. She will resist and even dislike the post. The most effective method of teaching your cat to use her post is through lures and rewards. Never take this for granted.