This is an arab mare. Not a big horse. She is ridden in a french link snaffle and she is uncontrolable?? I seem to have that straight?
How hard can she possibley be?? Get that french link out of her, I much prefer a straight solid mouth piece and a running martingale. The martingale does nothing UNTIL she throws her head up and tried to escape the bit through hi headedness. Unless you have tried on don't knock it until you have. The running martingale does nothing unless it is needed and then suddenly the martingale doubles the force of the pull giving you a big advantage.
Neck is the curb bit like I already suggested. The horse can not escape by lifting her head. The curb strap makes sure of that.
These problems stem in the beginning by no respect for the bit. A horse needs to respect the bit, teach her respect and if you have to hurt her to get respect so be it.
These problems do not exist in my world because I don't let them escilate to that point. The minute I see a horse disrespecting the bit I teach it respect.
You do not keep a horse light, respectfull by riding all the time in the gentlest bit you can find. Even the best trained horses need tune ups a regular intervals.
If that mare were to lean on me with say the STRIAGHT solid snaffle I AND a running martingale I would hit her with everything I had in my legs, my back my arms and set her right back on her haunches, yell at her and then quickly release. She would learn respect, learn not to lean of me, learn not to run through anything I am riding in.
I love riding horses like this, one time only but I love teaching manners.
She is little, you can overpower her with a little help.
Teach her respect.