Join Date: Aug 2008
Location: Canberra, Australia
She's not too old to learn, but remember that if competing in hack classes younger horses may look and move better than her, depending of course how she looks for her age. Dressage is just the basis of riding and any horse can learn it.
When you say flex I'm not sure what you because it sounds like you want her to soften and go "on the bit". Remember that being on the bit isn't just about head carriage, its how their frame rounds up so its about their whole body.
I wouldn't use a martingale. Firstly, as far as I know, you can't use them in the dressage ring, and if you could use them in the hack ring it would probably count against. Secondly, its not going to fix any problem, its just going to hold her head down.
I would do lots of circles and transitions, she should be able to do everything in a snaffle, I wouldn't go to anything harder. Try and get her responding to very light hand aids and make sure you don't try to pull her onto a contact. You might have to start getting her relaxed and working with her head down on a longer rein then one she can consistently hold that start shortening the reins little by little and lifting her head up.
As others have said, having right outline takes a lot of new muscle and if a horse is not used to it they can hold it for very short times.