need help fitting my thoroughbred mare!! pleeaase!?

It's kinda hard to tell without really seeing the back or anything. I'd go quarter at first since she is Thoroughbred, they tend to have more narrow withers. That way you know to go up or down if it doesn't fit. What I'd do is ask your friend what her saddle is if it fit and go from there.

"Completely objects to the whole flexion and bending and collection thing" - this means there is pain or you need to seriously sort your riding out and have lessons.

Her saddle may be custom fit, but she can change shape - get the saddler to check it. Also get the physiotherapist to give her the once over and get the chiropractor out to check her back. Also have the dentist check her teeth.

If there is nothing wrong and in your lessons the instructor says you are riding fine, then you need to man up and get after her - sit tall, kick on, give a flick with a schooling whip and growl at her to show her you mean business.

Don't give up - if you can't get her to go well riding her English, you will have problems in Western too. Both types have the same foundations and it's obvious something is wrong in English and that needs to be sorted - you can't do anything without the basics.

Oh, and only a saddler can fit a saddle to your horse correctly - we can't tell you over the internet.

I saw your other pictures and I'm concerned as to why you've wrapped the chain lunge line around her nose...?

It sounds to me that you're giving up far too easily. She knows if she bucks and rears she gets the comfy western saddle. Get the dentist out, she may not like pressure in her mouth, there may be some sharp teeth that need rasping. Next get the saddler out again. Then a vet. Rule out all the possibilities before you change to another style.

Hope this helps:}

Horses change shape as they age or according to their conditioning. Just because a saddle is custom made to fit a horse, that does not rule out the possibility that it is now a source of pain.

Barrel racing certainly requires strength and flexibility, bend and ability to engage the quarters, and no horse is fit for athletic performance when unable to develp his/her body as an athlete. This plan of yours to use the horse for barrels because you can't get her flexible, supple, and balanced needs some rethinking. You can't even develop the muscles she needs for this work without getting her to engage her hips. Without properly conditioning her, you are just asking for major injuries to occur.

You need evaluations by an equine vet, a professional saddle fitter, with evaluation of the bit you are using and of her mouth cavity to rule out pain issues.

Whatever you do, I strongly advise against attempting barrels with this horse. My horses were fully trained and conditioned in dressage and finished in western performance, and only then did I feel they were conditioned and developed adequately to train for barrels. It is a very demanding sport, and your horse should be in top athletic condition for it.