10 years old is certainly ripe old age. Congrats on being able to keep her alive that long. :)

First of all, a limping chicken could mean anything from and in between, botulism, being egg-bound, Marek's Disease, bumblefoot, slipped tendon in her hock joint, worms, or just a vitamin deficiency. From what I've seen in my chicken experiences, chickens get probably as many problems as humans.

Also, a pic would be helpful, just to access the overall condition.
It's a very good sign, that she is eating and drinking well.
Chickens are very hardy, and have a great 'will to survive'.

Eliminating couple of things;

Is there a black spot on the bottom of her foot?
If you palpate her rear a bit, under the vent, so you feel anything hard?

Splinting something shouldn't be your first resort.
Adding a teaspoon or two of Apple Cider Vinegar will help keep her resistance up and maintain general health.
If it's worms, you'll need to add a bit of Diatomaceous earth to her feed in order to kill them.
If it can be narrowed down to a slipped tendon, then I'll search out a page in my bookmarks about Chicken Podiatry for you to look at.

Hope this helps. :)