Turnout is best really, as she will be moving around and burnign calories instea dof stood still in a box. Use a grazing muzzle like the Greenguard for her, which restricts grass intake by 70%. She can wear it 24/7. If her grazing is restricted long term it might be an idea to give her a balancer such as Top Spec Anti Lam. She will get all the vits/minerals she needs but with very few calories. You can feed it alone in a bucket, no need to add any feed.

Start with light exercise in walk only for at least 4 weeks, gradually building up the time, then add some periods of trotting, for another 4-6 weeks, again, increasing the periods of trot, then when she is coping well with that, add some canter work.