This biggest issue you might come across is if he's spur trained, otherwise known as "spur-stop". Some big time pleasure horses are trained to slow down or stop if both spurs are put on, and they usually "bump" with their legs to go forward. The good ones are also really sensitive to bit pressure. They also are built to go slow, verrry slow. And they also have a very low headset. You might want to make sure that's really what she wants because it's hard to turn them into speed horses if she changes her mind.
But that's just if the horse is a professionally trained, breed-showing WP horse. If it's just someone's open show, backyard "WP trained" horse, it will probably just be the same as any western horse, maybe with a little more control. (No offense, my horses are trained in my backyard too, haha)