I've been riding her bareback very lightly, lots of walk, some trot, and just a bit of canter (because she always wants to). We do lots of bending exercises, and walk and trot over poles. Once the ground is in better shape, we're going to do some light riding or handwalking on hills.
She's stiff in her hind end and really needs to build up her strength. She's so uncomfortable picking up her back legs that we can't even pick up her feet to clean or trim them. I'm not sure how much of it is actual balance problems and how much is in her head. I think it's a combination of both. But, she's always very happy to be ridden and lets you know how thrilled she is to be out. She always wants to go go go.
Any exercises you know of that will help strengthen her hind end without pushing her too hard? We mostly work indoors in a sand arena.