Hi Tracy!
How exciting that you are planning your upcoming trip to Walt Disney World! My daughter is also ten years old and she was awaiting the day that Walt Disney World would consider her an adult! She feels so grown up now!
You can certainly purchase the
Walt Disney World tickets now and purchase the adult ticket for her, since you are planning for the trip when she will be 10. If you plan on visiting earlier, she can still use the ticket, that's not a problem. The opposite is not true though. You cannot purchase a child's ticket and then visit after your child turns ten, and have her use a child's ticket.
Keep in mind also that if you purchase the
Disney Dining Plan and buy an adult ticket, she will have the adult dining plan, which is great because she can order off of the adult menu and have many more dining choices.
While you are at Disney, don't miss
Frozen Ever After! She will love this new attraction.
I hope you have a magical vacation!
Magically,
Stacy