There are a few cool things you could do!
1. Order a basket to be sent to your room. A birthday basket. I use
www.memoriesbybetsy.com. She does a great job and will get you whatever you want!
2. As you said... you can order a cake. You can get a cheaper cake than $100. You can get a Mickey head cake for $48 which is pretty large and very good. It is either chocolate or vanilla.
3. You can order her a Cinderellas Slipper (chocolate) at a GF restaurant or at Cinderella Royal Table (if you are going there) for $12.
4. I don't know if she is a Disney girl, but you could take her to the Bibbidi Bobbidi Boutique and have her princessified! I think for just hair and make-up now its $50.
5. Order something from
www.disneyflorist.com. I would prefer using Betsy but the Disney Florist is the only one who can include food/snacks with your order. They also do floral arrangements and other such room surprises.
6. Do a wishes cruise!
7. You can have Gifts of a Lifetime do a scavenger hunt in her favorite park! They will do one customized to her or whatever you choose to do!
www.giftsofalifetime.com
8. Just create the special day for her. get her a tiara and a birthday pin. Almost every where you guys go Cast Members will tell her happy birthday. Take her to a special restaurant, some places will give her a cupcake with a candle anyway... and you don't have to pay for it. Take some gifts with you and have a small party back in your room.
9. You could do a special tour. Check out:
http://disneyworld.disney.go.com/tours-and-experiences/ Lots of cool stuff to do!
Just a few thoughts! I am sure it will be special no matter what you do!
Gina