Hello, Melanie!
Welcome to planDisney, and congratulations! I'm so glad you want to celebrate such an important family milestone at the Disneyland Resort!
Since reservations seem to be completely booked for your dates and you need the certainty to plan, I have a suggestion for you. The
Disneyland Resort has separate park availability calendars for Guests visiting with regular theme park tickets and for Guests staying at Disneyland Resort Hotels.
So if you can't find theme park availability for regular theme park tickets, you can check the
Disneyland Resort Hotels availability calendar. If that date is open for Disneyland Resort Hotels Guests, you can
book a room, add your niece to the booking and make your park reservation for your niece. How does that sound?
I think this would be a fantastic way to celebrate. Let us know if you need any other insights before your trip!
May the magic be with you,
Julie