I can see the technical problem that the stories are visible to people who aren't logged in, so even if a specific account is not allowed to read a chapter, they could still see it after logging out. So the system to achieve what you ask would require an account just to get to see the stories and then blocking one person.
...And that would be a rather heavy handed change to the existing system.
If the main gist is that you want feedback on the chapter and possible rework done before revealing it to the main recipient, just ask around for people to be test readers and send the text to them. Then after feedback publish it normally.