You know Feathers,
Those older guys can really scare you sometimes over nothing. Our 24 yr old (the Appy) had a rough winter and I had the appointment to put him down and everything-he wouldn't eat, lost a TON of weight , vet couldn't find anything else wrong-teeth, fever, ANYTHING(he'd bowed his tendon late fall -an old war wound for him anyways) and the cold had been hard on him, even with blankets and extra food, and lots of my time freezing my butt off trying to tend to that leg and the vet had an emergency and couldn't do it that day, and I'll be darned if that horse didn't suddenly decide life was worth living again and he's not only doing better, but you would never know he got hurt now. :roll: He's sound, and gaining weight. I was part mad at having gone through all that worry of "am I doing the right thing or not" and relief that the old fart was just fine!
My thoughts are the bute that I was giving him for the tendon gave him ulcers and he didn't want to eat..and that sprialed him downhill. I'm not sure what suddenly made it all better, but I'm glad it did. All that starving did a number on his hair coat this spring, he shed out bald before he grew in the summer hair, but he's sleek and shiney now. Back to his old, pushy self. Still needs a more weight, but he looks a lot better! He acts younger than the 7 yr old.
So don't get too worried just yet over your girl. Sure, have the vet check, but it might just be something simple and manageable along with the age factor.
I edited to add a recent picture of the old guy-like I said, still needs more weight but he was a rack of bones and he's gained a couple hundred pounds back already. (I don't normally leave halters on them, but in this pic they are in the front yard-and the driveway is wide open but for a string I put across and the halters are in case they figure out that string isn't a hot wire!)