For a start, they are separate databases, so the information from the archives does not necessarily transfer over to the forums. Both registrations are quick and easy, providing you follow the instructions, so it really shouldn't be difficult.
The author posted her stories before she was 18, and since this is an adult-only site, the stories were removed along with the invalid account. Since she is now over 18, she is welcome to create a valid account and repost her work.