Have you tried to block her sight backwards? Horses generally don't like to reverse if they can't see where they are going. 

Hi I have  tried the  blinkers but she  gets  in  her  head  go back she  goes at high speed 

Hi. Can we have a bit more information please? Does your mare do this when being lead or ridden or both? Where does she do it - always around the same place or time ( 30 seconds after leaving the field/yard, 2 minutes, 30 minutes ) or is it seemingly random? Have you any thoughts on why she so desperately wants to stay & doesn't want to go with you? It maybe this is just a learned habit resulting from a bad experience somewhere else with someone else. Do you know her history or a specific event that prompted her problem? We want to help you & your mare so please help us help you. Cheers, Jo.

Hi jo,have the mare about 4 months dont know much about her past ,she is fine inthe stable and field.when been ridin she will try and stop but a bit of leg on and voice she will go forward .but when she comes to a new area ie a very small stream or a cows in a field its brakes on and a high speed reverse so much her hind legs goes under her ,full xray of her back is fine teeth done no problems that way .thanks for your reply

Hi. Sounds like she is genuinely ' very green ' - REALLY INEXPERIENCED. In Britain all equines have a passport once 6 months old so, together with the microchip, we can see their age ( in theory - there are problems with accuracy ). Did you have her vet checked? Did you ride her & see her ridden before you got her? I think she is either 8 but was recently only trained for riding and/or only ridden in an arena or is possibly much younger. It doesn't matter which, my advice is the same. She is NOT BEING NAUGHTY. She is GENUINELY TERRIFIED. Horses that balk or nap don't fall over! This mare needs your love & understanding. She will grow mentally & become a true partner but you are going to have to put in some considerable effort - because someone else either hasn't bothered or past her on to you before they had time to. In my view you have rescued this mare from an irresponsible person who has put both you & this mare at significant risk. You are both lucky you have not had a serious accident. 
.
I see you have been studying the lessons on the Uni. You need to work with this mare from the ground, controlling your breathing, being very aware of your body language & building trust. Ideally working in an arena or roundpen but if you don't have access to such facilities you can work in a corner of the field. Join up / follow up to start the relationship. Use a dually halter not a bridle - even though I assume you've used saddle & bridle to ride out. Work with her at home ( no riding out ) until you both have a basis of confidence in each other. Then, if you can, ride out with a friend who has an experienced horse so your mare has a good example to follow & equine moral support. Keep in touch & let us know how you are progressing. Cheers, Jo.

I think Jo has given you excellent advice, any horse that you buy I think should always have join-up and work in the dually halter too,if nothing else but,to give each of you a chance to get to know one another with choices as well. Choices the horse may make and choices you may make.The ideal time would be to do this before you buy.It does tell you alot as well about each other.Ground work is the most important part for this mare,as well as for you.Have lots of fun getting to know each other,learn to breathe,and learn from this mare as to what she is thinking then you will have a partnership for life.The Best to you,Angie

Hi Angie,  my advice to you would be to follow what Jo has written as she speaks from a wealth of knowledge and empathy.  Empathy is what I would concentrate on in your relationship with this horse.  Horses are huge information gatherers especially if that information is empathic.  It sounds like your horse some has fright gremlins that are getting in the path of her ability to relax and enjoy your partnership as a rider.  If you can go back to doing some ground work as Jo has suggested, that should level the playing field for you to have success.  If this was my horse, I would start with teaching her how to lower her head and relax with her movement on the ground [shoulder-in exercise] with an emphasis on showing her how to lower her head and stretch into the movement.  When a horse learns how to move in a relaxed manner, everything they do gets easier.  Retraining your horse from her back really would be a challenge for the best of horseman, so please consider doing ground work.  Get control of her feet from the ground and work hard on your timing for the release of pressure ie. when you ask for a foot to move, release as she starts to pick up that foot.  This will change how your horse responds to your cues.  In time, as you become more precise in YOUR reactions [the release] she will see you as the leader and gremlins will be forgotten.  Good luck Angie and enjoy the journey.

Bud

P.S. to see the shoulder-in movement done on the ground: go to arttoride, first work in hand--u-tube.  Mr Will Faeber  will guide you on the how and whys..