With a 4 year old, you have to be very consistent and break everything down into simple steps. Once your dressage instructor teaches you how to properly cue her, just be careful to continue to cue her the same way when you are schooling between lessons. Take advantage of the fact that you are new to dressage to train both you and your horse consistently. Just take it slow until both you and your horse are on the same page about your cues. If you find her getting frustrated about something, take a step back and give her a mental break. The last thing you want to do is drill the same thing into a young horse. Keep it fresh and interesting for her. Dressage is fun and very addictive. I'm sure you'll love it!