Since Aart tagged me I'll respond. I probably would not have seen this otherwise.
Aart I have a question, heard from someone once that older chickens aren't as good for meat, the flavor and toughness of the meat apparently is different (thought maybe they might not know how to slaughter and clean chickens appropriately...?)
As chickens age the meat changes. It gains texture and flavor. It's really apparent with cockerels going through puberty when those hormones hit but it happens to the girls too, just a whole lot slower. Most of the chicken you buy at the store are Cornish X meat birds, slaughtered at 6 to 8 weeks of age. Those are still extremely tender and frankly don't have much flavor. But if that is what you are used to you may not like the flavor or texture of an older bird. Many people don't.
You can cook and eat any chicken of any sex and age. The French developed Coq au Vin, a way to make a gourmet meal out of an old rooster, the toughest and strongest flavored chicken there is. It's not so much about slaughter and clean but what you do afterwards. As Aart mentioned aging to get past Rigor Mortis is essential. Then it's how you cook it. There are a lot of different recipes for that. Chicken and Dumplings is a traditional way to make true comfort food and stretch one chicken to feed a large family. Aart mentioned pressure cooking, that's one way to tenderize the meat. Chicken stew or chicken soup is a great use for older chickens, just cook them long and slow at a simmer, never let it come to a full boil. You can use a crock pot set on low, again long and slow.
If nothing else make chicken broth or stock. An old rooster makes the best but an older hen does a respectable job. It will still be better than the broth or stock you buy at the store. Even when I cook younger chickens other ways I save the bones for broth. When I butcher I save certain parts like the back, necks, and feet for that broth. I put that in a crock pot covered with water and flavored with herbs and cook it on slow overnight, which usually translates to 18 to 24 hours. I strain the liquid out, de-fat it, and have great broth. And I pick the meat out of the solids to get delicious meat great for tacos, chicken salad, or to add to soup. I often eat in on a sandwich for lunch. Some people think that meat is too soggy (too tender) to use like that but I think it's great.
And how old is too "old" for chickens, at what age do you slaughter them. I have an older hen (don't know her exact age, wasn't mine originally) and I see she takes a long time laying, but she's a great mom,
To me they are never too old if you know how to manage them. When hunters bring ducks, pheasant, or geese home they have no idea how old they are but they still cook and eat them.
I'd say she's also a bit chubby but my husband assures me she hasn't really gained weight (I dubious about that...)
All hens (and pullets) pack on extra fat before they even start to lay. If you slaughter a hen and a rooster you'll be amazed at how much difference in fat there is. That fat is put there for a hen to live off of while she is broody. That way she can stay on the nest incubating eggs instead of having to be out looking for food and leading predators back to her nest. They do lose weight while broody but that's just fat put there for that purpose. That may be part of what you are seeing.
Possibly something else. Many hens are a lot more feathers than body. Some broody hens pluck out some breast feathers while incubating. When they molt you can often see a tremendous difference in apparent body size. You think they are really thin and in bad shape. Nope, you are just looking at their body normally hidden under all those feathers.
Hens can have different body types too. Some are just naturally rounder than others. Some seem to be wearing pantaloons, big and fluffy back there, while others have a trimmer, more game hen type look.
If she is living with the rest of the flock and eating what they eat and has done OK for this long she's probably OK.
either dogs or possums or cacomixtle, we're not quite sure). 
My current home is in a very sought after market and near everything + we wouldn't have too much concern over keeping stable jobs if life happens.
