I see so many describe how they feed; hay by the flake, grain or supplements by the scoop, but the actual amount as in the amount being fed by weight is what is most helpful. If your mare's ideal weight is 1,000 lbs., then whatever she's receiving needs to be addressed, in my opinion, by the amount you're feeding by weight. A flake can weigh anywhere from a pound to several lbs., for instance.
If she's cleaning up all of her hay between meals, I would think she requires more hay, or free choice hay. If the scoop you're describing holds 2 lbs. Of senior feed, for instance, you may need to double that amount for a senior who is being ridden even lightly every day. I feed by weight because it's the only way to get what the horse needs into them, and after you're using to weighing feed, whether it's hay or supplemental stuff, you get a good feel for it in no time, and no longer need a scale to go by.
If she's not wadding hay or dropping grain, her teeth are probably ok.