I agree with everyone else that the hen should be put down if she is suffering, and especially if he does not have the time and ability to nurse this pullet. If he were an older retired person who stayed home, she might be able to live with a lot of supportive care. There are very expensive wheelchairs available for chickens who can still move their legs some, and a handy person could build one. A sling is much easier to make, and those can be useful for short periods throughout the day, with periods of rest and stretching in between. Here are some links for wheelchairs:
https://chickentherapychairs.weebly.com/
https://www.handicappedpets.com/walkin-wheels-duck-wheelchair/
Here are a couple of pages of easy homemade slings:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
https://chickentherapychairs.weebly.com/
https://www.handicappedpets.com/walkin-wheels-duck-wheelchair/
Here are a couple of pages of easy homemade slings:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/