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... ;)
She is a little more fat than muscle at the moment since we got back from anglesey and she had a week off (about 2 weeks ago?). There isn't much grass on the field so I have been feeding her a little more than usual the past week or two also because I havent got a scoop at home so I just kindof pour the feed out I think I will do some canter work in the arena as well as hacking and muscle her up over the next week so she looks purty for the show :) but she doesn't look neglected? Lol