I am early in Season 5. I'm mentioning this, because I'm trying to avoid spoilers.

I a season 4 episode, I saw Sara Gilbert had a "story" credit.

https://www.imdb.com/title/tt0688776/fullcredits?ref_=tt_cl_sm#cast

Did that happen much? That a teenage actress had a story credit?

Did it happen in any prior episodes, to the one I linked?

It certainly happened to Roseanne's children. Jessica is credited for writing one episode, but it's an episode in the series' future.

Thanks.