What is some good themes for a turning 15 years old? Or what kind of anniversary should we have? Maybe for example: dormant party, movie party. 
I feel we can do one of the following themes:

Pool Party or beach theme
Luau / Hawaiian ThemeHere are kinds of things you need, depending on beach, pool, or luau themes :
Easy sand Cup
Cheese & Fruit Kabobs
Thematic Cake recipes
A cheap, quick and simple food, Pizza!

We love pizza! Make sure use pepperoni (some girls not want a bunch of things on their pizzas), and at least one cheese pizza (for the oddball vegetarian). Serve a simple beverage, such as 2-liter Sprite, Coke, and so forth. OR some Kool-Aid or lemonade for them to drink. AND do not forget ice cream if you cake!

Send the invites at least a few weeks in advance, and have many activities to play, so weare not bored. Thing the worst that can happen when a party goes is bored guests!

Have some time appropriate movies to watch (perhaps even ask all guests to a favorite movie or board game). Have some favorite music playing as guests arrive and have a lot of snacks ! 

Have everything prepared so that when the guests start arriving, you can individual / group photos of them with the birthday person. AND at the birthday person feel extra special, decorate a special chair.

Do not forget to send thank-you notes for friends … BUT make sure that the birthday person is doing them. They must show its gratitude, weather they brought gifts or not (they will simply thank them for her party).