Yes, people vitamins are fine for poultry. With B-vitamins, it's hard to overdose as the excess is excreted in the urates. And vitamin E will help repair neuro function, so @Eggcessive 's recommendation is a good one.
Yes, they can recover. You've not only done wonderful care and treatment for your chicken, but you've certainly got a splendid mastery of English and expressing yourself in this language.
I have a suggestion that could possibly heal your hen's legs further. Give her vitamin B complex, the...