Work her in a good frame, you can start working her in side reins if you know how to use them and always encourage her to reach into the contact and use her back when riding her.
And also, loung your horse once a week
A great exercise is the long and low. http://stridesforsuccess.com/long-and-low/
Correct work, hill work, transitions, serpentines etc etc. Get the horse using it's back and the rest will follow :)