Oh, I'm sorry to hear that
Yes, it's common for laying hens to have reproductive issues - it can happen at any age really.
If she's unable to walk now, then it may be time to consider putting her out of her misery. I know you care deeply about her, but she's been through a lot. It's up to you of course.
The only way to really know what's been going on with her is to have a necropsy if she dies. Having a professional one done by your state lab is going to give you the best information. You are in CA, so UC Davis is your lab. I'm not sure how much it costs but you can call an ask. Alternatively, you can do your own and see if you find anything obvious. Sometimes a hen may have other issues like Fatty Liver Disease, a heart condition or ??? You may find something or you may not.
I don't think you caused this...I don't see how