Subtle ways to show your dad your stepmom is a horse afterall
Pet her forehead and wait for his reaction when he sees how much she loves it.
Keep sugar cubes on hand for a secret little treat to enforce good behavior.
Treat them to The French Laundry but meet with Thomas Keller beforehand so that every course is just alfalfa cooked a different way.
Gently feed her an apple, whole.
Cover their bedroom with hay and wait for her to take a bite.
Watch The Godfather together and wait for her to say something when her sister cameos in that one part.