Hi Heather,
Your little princess is going to absolutely love Bibbidi Bobbidi Boutique! It's a "must do" for my little girls on our Disney vacations!
Since the Magic Kingdom is currently scheduled to open at 9am on 4/19, and you need to check-in for your reservation 15 minutes early, you really won't have much time to explore. I recommend pausing to visit with characters that are generally right inside the gate greeting guests or simply enjoying the stroll down Main Street, USA towards Cinderella Castle. If you arrive at Bibbidi Bobbidi Boutique with some time to spare, your daughter may want to ride on
Prince Charming Regal Carrousel or watch
Mickey's PhilharMagic. First thing in the morning, these attractions generally do not have a wait for them.
Depending which package you have selected, you also may want to head to Bibbidi Bobbidi Boutique early so she can choose her outfit.
Hope this helps and that you have a wonderful vacation with your family. Please let me know if I can assist you further,
Kaylene