I always recommend video of your child being most herself. When you see an HG+ child in action, I think you know it.
I also always recommend that people applying remember that the goal is NOT to show that your child is GT. The goal is to show that your child is HG+, so you need to demonstrate abilities exceeding MG. There's a difference there. Think 3+ years above age-level.
Video of her composing and then playing her music could be good. Tables and charts she has created could be good, especially if they exceed the planning ability of even most GT kids her age. Do be sure to send a good bit of academic work. You can even send video of her thinking through something really hard, then also include the written work she did while being filmed. That gives them both a look at how she works and at the product itself.
