She looks fine, but it never hurts to feed em up a little... I prefer mine get fed a little more to avoid them losing weight in the winter months, as they use alot more energy trying to stay warm- to me that's easier than letting them lose a little and then having to fight to get the weight back on.
Agree with others that she looks fine. Disagree very much with Pepper that it 'never hurts to feed em up' though. Horses, like people, can indeed afford to put on extra weight & stay healthy, but retaining 'good condition' long term without regular 'hard seasons' to use up those fat stores can very much hurt us, in the form of type 2 diabetes/insulin resistance & in horses this is a common cause of laminitis.
Obviously if your horse is 100+ pounds overweight, feeding them up isn't going to do them any justice.. that's just common sense:)
Me personally, I like my horses going into winter with a little fat over their ribs. Obviously I want to be able to feel the ribs, but I am more comfortable having to work a little to feel for them when my horses are outside in all sorts of wet cold weather.