Welcome to the Moms Panel Kathleen!
Your daughter is going to love the
Bibbidi Bobbidi Boutique. If only it had been around when I was a little girl going to Disney World.
Once you arrive at the gates and go through security, head towards the turnstile for early Dining Reservations (it will be listed on a sign above the turnstile and any Cast Member can direct you to it). Bring your confirmation number with you to show to the Cast Member. You can then head down Main Street U.S.A. towards Cinderella Castle.
You should plan to arrive at the Bibbidi Bobbdi Boutique 15 minutes prior to your reservation to check in. I'd also give myself at least 15 minutes to walk to Cinderella Castle once I was through the turnstiles. I must admit, it is a great time to be in the Magic Kingdom for photo ops because of the very low number of Guests in the park so take advantage of it.
If you're staying on property and taking a Disney bus to Magic Kingdom, you should be fine arriving at the gates 30 - 45 minutes prior to the reservation time. If you're driving your own car, I'd allow an hour from your reservation time to get from the parking lot over to the Magic Kingdom and down to Cinderella Castle. The Express Monorail may not be running at that time so hop on the Resort Monorail.
I just know that your little Princess will have an amazing time. Please feel free to visit with any other questions. Wishing you minnie magical memories :-) Allison