LAST UPDATE
Well, it's done.
She'd begun having small intermittent seizures and along with all her other problems, I decided the kindest thing I could do was end her life.

I had read a thread/post in the beginning of all this, on the correct way to break the neck (it was described perfectly) but couldn't find it again.
I decided to try YouTube, after having read another post that mentioned watching videos there, and I couldn't believe it, but yes they had videos on several different methods. The ones I watched were short, direct, and respectful of the bird. It may sound macabre, but I'm thankful they were there.
I'm still a little shaky, I wanted to get this done asap and not think about it for awhile... I've never had to kill something that I'd spent time with and cared for before. The very few times I've personally euthanized an animal in the past, it was always a wild one who'd been so seriously injured it was obviously going to die anyway but they were suffering so much I wanted to help them end it asap. In the past, I've always taken them to the vets to be euthanized. Just last week we had to put a beloved cat down. RIP King Henry.
Anyway, I chose (what I think is called) cervical decapitation. My son was there as well. For a number of reasons I felt it would be good for him to learn from this experience as well.
Unless someone requests it, I won't go into too many details, but I think it went as well as it could for a first timer.
One last Big Thank You to all who helped! Either by sharing your knowledge, support, anecdotes of your own, or all of the above. It made a very stressful situation easier to deal with and I learned so much.
Wishing you all the best and especially for happy healthy chickens and families