She doesn't look bad at all. :P
I'd suggest just working out with her (heh... on a treadmill
), just to have more muscle, and less fat. But she seems to be a good weight.
Weight truly does depend on the horse. Some horses you think "wow... they look kind of chubby", when in actuality, it's their healthy weight. Muscle also weighs more than fat, so if your horse is muscular, and heavy, it doesn't mean that the horse is fat... just muscular. :P
It truly depends on the horse. But I'd have someone else tell you that REALLY knows what they're talking about... unlike me... ;)