Denny Emerson, one of the best eventers and trainers of... well, ever... conditions all his performance horses from scratch by getting on and JUST walking. And walking and walking and walking and walking. Weeks and weeks and hours and hours of walking all over the countryside. Eventually he builds from there but that walking is critical to the plan.
I wouldn't be looking to do anything more intense with this horse. She's overweight, she's coming back from being in the verge of laminitic, and hasn't been used in years. Lots of walking and exploring will be good for your bond, too. And it should help with the weight loss without putting too much stress on her body and joints while she gets stronger.