WARNING: This article has spoilers from Black Lightning season 4, episode 8, "The Book of Ruin: Chapter Three: Things Fall Apart."
The Black Lightning creative team or Warner Bros. TV.
Despite that, it seemed like Kariuki was now the Arrowverse's new Jennifer Pierce from now on. But it may not be the case after all, as Black Lightning season 4, episode 8, "The Book of Ruin: Chapter Three: Things Fall Apart, is teasing something else. Lynn Stewart has run multiple tests on Jennifer ever since her rebirth, but the results from Jennifer's particle sustainability test came back as "uncertain," causing concern. Lynn immediately compared Jennifer's stats before and after she was reborn, revealing that Lightning's original form was stable while her new one is not. Despite the problematic results, Lynn decided not to tell Jefferson, assuring him that everything is fine.
Laura Kariuki being a temporary replacement would explain why there has been such secrecy about the Arrowverse recasting after McClain exited Black Lightning in the middle of the final season. A popular theory about McClain's initial announcement was that she would be in a few episodes at the start of Black Lightning season 4 and then in the last remaining ones towards the series finale. But once Kariuki took over the role, it was always strange how there were no post-mortem interviews or any talks from the creative side. Perhaps they did not say anything because JJ's form would never be a permanent Arrowverse recasting.
Another moment in Black Lightning hints that this recasting isn't permanent: when JJ refers to Jefferson as "daddy." Jefferson notes that she has not called him that for several years, with her quickly saying, "Gotta change up every once in a while." This response had a suspicious vibe to it, possibly setting up that this is not the real Jennifer Pierce. Visually, she was reborn with another girl's looks, but so far, the assumption was that this was just a physical side effect. It's possible the truth is more complicated, and that this Jennifer is from another universe with some personality changes. Jennifer was the only character in Crisis on Infinite Earths who interacted with her counterparts from alternate worlds. It would not be too strange for the Arrowverse if Jennifer's original looks somehow got to another Earth, but with a different girl looking like her.
Creatively, it would explain JJ's test results, and it would be a way for Black Lightning to write out McClain for a couple of episodes before the end. It seems unlikely that Black Lightning's final season would end somehow with JJ dying from her body blowing up, but given how worried Lynn got from seeing the test, something is happening to Lightning. While Kariuki's JJ has been a lovely addition, it was always a little strange to recast a principal character in the middle of a show's final season. Even though Black Lightning showrunner Salim Akil has been open about the Pierce sisters showing up on the spinoff series Painkiller, if it goes forward, it does not change how surprising the recast was. However, with the latest Black Lightning twist, perhaps the original Jennifer Pierce is on her way back before the Arrowverse drama concludes.