Why won't she turn?

I'm working with my new 10 year old mare and she's having trouble turning. She was left in a pasture for 6 months by her last owner and so we're still working out the kinks. She does forward, backward, all her paces perfectly. She turns right decently but left turns are difficult at best and impossible at worst. I can turn her from the ground fine (she's a model horse for ground work) but from the saddle she won't turn an inch. I don't want to do something wrong and mess her up completely so if anyone has an idea as to what's going on I'd love to hear it.

Check your tack and make sure it is good repair and fits her well. If your horse can turn left comfortably without tack, then I would suspect there is an issue with the tack or how it is fitting. Make sure there is nothing pinching or poking her - particularly in the shoulder, withers or along her spine. Make sure the bit fits properly and does not have any rough spots. Have her teeth checked by a veterinarian or equine dentist. Sharp points or misalignments on one side of her jaw can affect her ability to turn under saddle.

After you have eliminated any possibility of a physical cause, then check your own position, balance, alignment and posture in the saddle. All riders are better in one direction than the other. Get help from a trainer if possible who can work with you and your mare.

What kind of bit are you riding her in?

Are you trying to direct rein or neck rein?

How much training did she supposedly have before being left in the pasture for 6 months?

You need to work on shoulder control, right now you obviously have none. An excersises that my coach gets me to do at the beginning of every ride is to walk/jog/lope a small circle with their head bent to the inside, inside hand should be straight down while holding the rein and the outside rein should be loose, the horse at first will naturally want to fall into the circle but you'll have to use your inside leg to bump him back out when he tries this. The horse will do this because it's physically demanding for them, eventually it will become easy. It's great for building muscle and loosining them up as a warm up.

I use a loose ring bridoon its the bit she was trained with. She was fully trained and used as a cow horse for about four years before being put in the pasture. She used to do everything from cutting to roping.

Oh and I'm trying neck rein. I was taught to use as little bit as possible so as not to hurt the horse.

If she was that well trained, then I suspect her reluctance to turn is either a pain issue or you are sending her conflicting signals. Horses with that amount of training generally don't just forget after being turned out for a few months.

Have you had her teeth checked?

Are your sure your saddle fits and isn't pinching her anywhere?

Can you get video of you riding her so that we can see what you are doing and how she is reacting?

Do you have a trainer or a riding instructor in your area that you could maybe take a few lessons with to help work out some of the kinks?

Thanks for the help guys. I've got a vet coming to look at her next week to make sure she's not hurt and I'm going to start having lessons with the lady who trained her. I've had all the tack checked out so I'm hoping it's just me and not anything medical. Thanks again for the help!