Hi Sarah,
Welcome to the Disney Parks Moms Panel! How exciting to celebrate your daughter's sweet 16 birthday at Mickey's Very Merry Christmas Party! I am always delighted to greet a fellow North Carolinian.
As you consider if the dress might be appropriate to wear, review the
Walt Disney World Park Rules. Cast members at the park entrance would make a determination about her dress. The dress should not drag the ground. I would also caution against any dress that too closely mirrors a Disney princess dress. On a different note, I do wonder how comfortable she will be in that dress throughout the night.
Instead of wearing her dress to the party that evening, might I suggest that you gift her a photo session from
Disney Fine Art Photography or stop by, in her dress, to take photos at the
Disney PhotoPass® Service Studio at Disney Springs. Just be sure to check the hours for the studio on the dates of your visit.
If you have not done so already, I would consider
Memory Maker since you have such a large group. With one Memory Maker, you can capture all of the Disney PhotoPass photos from your visit. On one of our visits, we had over 200 PhotoPass photos and attraction videos.
Sarah, no matter what happens, spending time together at Mickey's Very Merry Christmas Party will make your daughter's birthday magical. Enjoy these moments with her and know that she is always your princess!
Magic, memories and Minnie Mouse hugs,
Donyell