Oh dear, I foresee pain, fear and bruises in this girls future and confusion, terror eventually the meat wagon for this poor mare.
I have nothing to lose or gain at all by giving advice. I am all for rescueing horses and giving problem horses a chance (Again see my Reeco threads here: Reeco update for those that are interested
HOWEVER I only advocate rescuing a horse when you have the experience, funds and time to put the problems right AND be willing to admit when the horse is too dangerous for you/anyone else and have that horse PTS if nessecary rather than pass the horse on.
In this situation Hybrid has non of the above and the only way it can end up is badly. The horse will be made worse by inexperianced handling and eventualy become a Dangerous and Vicious horse that even experianced proffessionals wont take on.
Hybrid - biting is NEVER acceptable I don't care if the horse is emaciated and not seen grass for years, biting is never acceptable, nor is kicking or rearing. Do yourself and the horse a favor, gift the horse to an experienced trainer and buy yourself some proper riding lessons.