Hi Andrea!
Thank you for bringing your question to the Disney Parks Moms Panel.
Your daughter will have so much fun getting treated like a Princess at the Bibbidi Bobbidi Boutique. I personally think that Disney should have an adult version!
You would probably have time for a quick trip to the Magic Kingdom if you get up early and plan to be there at opening. It generally opens at 9:00 a.m., but you could get lucky and it could be a day that the Magic Kingdom has morning Extra Magic Hours, which would mean it opens at 8:00 a.m. for Disney Resort guests only. That would be perfect!
You can find park hours on the Walt Disney World website calendar. Let's say that it opens at 9 a.m., though. You could get there by 8:45, watch the park opening ceremony, and get to experience a little bit of magic at the Magic Kingdom before heading to your appointment. I would definitely allow at least an hour of travel time from Magic Kingdom to Downtown Disney, so leave no later than 10:45. That's over an hour and a half that you could spend at the park. It's not a lot of time, but it would be a great start to your vacation.
Or, you could wait until after her Bibbidi Bobbidi Boutique transformation, and she would enter the park as a full-fledged Princess! Either way sounds great to me!
I hope this helps. Please let me know if you have any other questions.