Your vet might be able to give her a calcium shot periodically that might help, but I'd try feeding her a little yogurt every day and see if the calcium in that helps.
I know how you feel. I bought 25 total chickens last year, I lost 5 of them to illness or injury, one to a predator.
Despite my better judgement they were all named and became more like pets than they should have.
For each one I've wondered what I could have done better to have...