Definately youngstock, part bred arab and coloured classes.
She has lovely markings, and I agree with dannityla about the browband. Definately keep it plain so that the focus is on her markings.
I would go with brown tack. It tends to be preferred by judges and will go better with her colouring.
I would keep the bridle nice and fine. She is a fine horse so you dont want to cover up her features with big thick nosebands etc. Dainty horse - dainty tack.
And plait her up, leave the tail natural
It will be worth getting her as used to crowds, horseboxes and being around lots of other horses as much as possible. Most shows are quite hectic with a lot going on. The more used to it she is, the better she should be on the day, which will make your job a lot easier.
Practice getting her to stand still. If you can teach her to stand square at this stage it will stand you in good stead for the future.
Then you need to get used to leading her, from her left shoulder, firstly in walk, then in trot, making sure you perfect the art of turning right (easier said than done
)
Judges will take into account her age, and most youngsters are expected to get a bit hyped up at shows, but if you practice now, a well behaved youngster will impress the judges.
Perhaps a group of people at your stables could do a practice show. Start with 1 or 2 other horses, and all walk around your school in walk. Then line up in the middle and one by one, walk away, trot back and around the school, then halt and rejoin the line. When she is comfortable with this, you can add more horses to the equation to get a better feel for the show atmosphere.
I would tr and go to some winter shows and watch how people do it. Also, you could try sites like you tube which might have videos of people at shows. For what to wear, have a look at photos from major competions like HOYS etc on the internet.
Hope this helps x
Shes gorgeous. Sure you will do great!