While colleges have the budget to have a professional graphics department oversee the licensed used of their mascot to ensure it's consistency and integrity, high schools do not, and typically rely on generation after generation of student volunteer artists to create art for t-shirts, banners, the yearbook and other school projects. The problem is the lack of consistency. If you had 100 artists draw a panther, they'd all look completely different - each with their own style; and inconsistency is the single biggest factor in deteriorating a brand. The Pillsbury Doughboy doesn't look a lot different now than he did 50 years ago, and for good reason.
Get balloons and even a pull string princess party pinata that you can fill with goodies and use as a fun party game. Speaking of party games, Pass the Slipper, Cindy Says and pin the slipper on the Princess, are all fun games to play. You can also throw in some musical party games like Musical thrones or Royal Ball Freeze Dance for some dancing and magical ball fun. Use the Cinderella party songs like bibbidi bobbidi boo! Play karaoke using the Disney song lyrics. You can find them on CDs by the Disney Princesses themselves.
Don't draw or design it yourself, unless you are a professional cartoonist or graphic designer. Your cartoon brand mascot is the cornerstone for your marketing and brand building program. You'll live with it for a long, long time - it is well worth it to get a professional involved.