Immobile hair has become a specialty with two girls in ballet and cheer. I redo most their squad before games at this point
You'll need sports gel, bobby pins and non-slip elastics. Also some multi-colored or silver glitter and a small metal tiara (or two). I do reccommend planning to do it yourself because at some point, even if you pay for BBB, a redo will be necessary.
For fine hair you will need to gel damp hair into a high ponytail and secure tightly with elastic (preferably non-slip). Then-
Option 1: When my daughter was young with very fine hair I would divide the ponytail in half, braid each half and then twist each to form one bun around the elastic securing with two bobby pins (using an x-shape) until bun was complete. This made the bun look MUCH fuller
Place tiara and sprinkle with glitter. Finish w/ hairspray.
Option 2: As you secure elastic around ponytail bring ponytail back through and make a small loopy bun. Finish wrapping w/elastic until tight. Braid or twist the leftover tail securing with pins while circling the small loopy bun. Place tiara and sprinkle w/glitter. Finish w/hairspray.
I found the coolest glitter stickers with Disney shapes for my girls cheeks a few years back. I wish I could remember where... ugh!