Hiya she looks great if you use your driveing reins like tc said and also use your driveing saddle so the reins pass through.
You are doing great preping her up for future driveing.
Even though a little long reining is ok for your mare I would not put her to until she is about four and long rein and let her have her free time to grow as well so your keeping up her education while she has her recuation at play being a horse.
The driveing saddle will help your hands and you will have better controle of her as well and use your voice in the gates you want her to go walk trot and woah and stand.
Tc has got it in a nut shell also your nose band on your bridle to keep your cheek pieces in place.
She is an awesome mare for her age and as I can see it you will complement each other whilst out driveing.
Also if you drive her in a snaffle a twin wilson driveing snaffle would complement her as she is going well in a rideing snaffle and seems soft in the mouth.
I don't beleave in being a critic or critical but if some ones not sure and needs help id be glad to help and so would a lot of good people on here.
I wish you and your mare all the best and thanks for shareing your movie with us many thanks michael tricky and quincy.