Hi Barrel Racer,
first, it is quite cruel to ask a previous injured, old horse to still have a “heavy work load” and race around barrels. This mare should have a nice, easy workout everyday to keep her happy in her seasoned years.
That being said, I strongly NOT recommend any injections. The wear and tear of her pretty hard life can not be reversed but you can give her comfort for the years to come. I use with great success Back on Track products. Recently I added hock-wraps to my mare’s problem area. It works wonderfully. I also support her with a rather old-fashioned supplement called Myristin in combination with Glucosamine. In the winter, when joints ache more due to cold weather I add a quarter pill of Previcox (actually dog pills – ask your vet).
Be kind and give your horse what she deserves but don’t waste any money on injections.