Hey there Bianca and welcome to planDisney. Getting from place to place around the 43 square miles of Walt Disney World Resort is what Tiggers like me do best. Disney's Grand Floridian Resort & Spa, what a practically perfect in every way place to have a
Disney birthday celebration. Be sure to look into a
Mickey Mouse Celebration or Specialty Cakes for the event.
Your question has two parts. Yes, you may take the
Walt Disney World Bus Service from
Disney's Grand Floridian Resort & Spa to Disney's Hollywood Studios. All
Resort Transportation is complimentary to all Guests except for
Disney Minnie Van Service Connected by Lyft. The second part is that Guests of Disney's Grand Floridian Resort & Spa are welcome to the
Resort with complimentary or valet parking with a dining or event reservation. However, if you are only there for an event and you want to travel to a theme park then you may park your car but will need to move it after the event. By leaving your car in the parking lot you are possibly preventing Guests staying at the hotel or other diners from having a space. Again, moving your car is expected if you are only dining.
Bianca, I hope the birthday celebration is the very merriest of them all. Be sure to stop by the front desk of the hotel to pick up a birthday button for your niece and have her wear it all. Please feel free to
write me back directly with any follow-up questions or for other Disney vacation planning tips.
Enjoy making many Magical Memories.
~Jason