Hey there Karen, and welcome to planDisney!
How wonderful it must be to be one of the best grandparents out there for a toddler celebrating such a special day at Walt Disney World Resort! I bet she'd be delighted by all of the colors and decorations that would await her with a decorated door and I've seen this becoming more and more popular throughout my visits to the
Disney Resort Hotels and even neighboring accommodations.
At the present time,
In-Room Floral & Gifts provides guests with the opportunity to surprise their loved ones with treats and gifts during their stay but currently does not offer any door-decorating services. I had a quick look online and found that there are local vendors (some of whom are allegedly former Cast Members) who have been able to gain access to to the Disney Resort Hotels, and have even spotted them in the process of affixing balloons and streamers to a neighboring room during our most recent stay. (You might have some luck keeping an eye out for a group online comprised of former Cast Members called "Ear For Each Other" who have been able to continue to provide all kinds of things for guests at the Disney Resort Hotel locations including Shades of Green - though these are not officially neither products nor services offered by Disney.)
You might also be interested instead in gifting her a surprise experience through the
Enchanting Extras Collection, such as a
Capture Your Moment session where you can be part of safeguarding photographic memories for years to come that'll certainly last longer than decorations! Come back again soon to planDisney for any other suggestions to make her birthday extra-special or attractions that would be best for smaller-sized guests to enjoy.
May your granddaughter have the best day ever at the Most Magical Place on Earth!
Prince