Since Laura Powers has not been seen on Bleeding Gums Murphy (and Dr. Hibbert) on The Simpsons.
In more extreme cases, The Simpsons has been known to replace one character with another one wholesale. This might be because two similar characters serve the same function, making one of them obsolete and allowing the writers to merge the two. However, in the case of The Simpsons replacing Bart’s first crush Laura Powers with Superintendent Chalmers’ daughter Shauna, there is no obvious reason for the switch.
First seen in The Simpsons season 4, episode 8, “New Kid on the Block,” Laura Powers was Bart’s babysitter and earliest crush. Although she hasn’t made any appearances since, Laura and Shauna Chalmers have a suspicious amount in common. Both were babysitters of the Simpsons kids, both were rebellious teens, both dated the ing character Jimbo Jones, and both made a big impression on one of the kids before breaking their hearts. While The Simpsons replacing Mrs. Krabappel made sense due to the untimely death of her voice actor Marcia Wallace, there’s no apparent reason for the animated sitcom to replace Laura Powers with Shauna. However, since Laura Powers hasn’t been seen since her debut (outside of background cameos), and Shauna was briefly Bart’s girlfriend before she dumped him for being too young, it’s fair to say that Chalmers’ daughter essentially replaced the earlier fan-favorite.
The reasoning for this switch could be that Shauna Chalmers is voiced by a Simpsons regular, Tress MacNeille, while Laura Powers was voiced by a special guest star. Since Laura’s voice actor Sara Gilbert is busy playing a lead role on the The Conners, replacing her character with one played by MacNeille might allow The Simpsons to revisit the newer character more often than they can afford to bring back Laura. However, even with this explanation in mind, the switch is a strange one. After all, Laura appeared in season 4 while Shauna didn’t make her debut on The Simpsons until season 20. Even then, it wasn’t until season 23, episode 18, “Beware My Cheating Bart,” that Shauna got an episode of her own, so evidently, there was no pressing need for The Simpsons to replace Laura.
However, the fact that Shauna proceeded to break Bart’s heart by dating Jimbo Jones and later became his babysitter made her trajectory bizarrely similar to that of Laura’s Simpsons story. This could simply be a Simpsons mistake, a case of the show rehashing a successful earlier episode, or a coincidence. However, the striking similarities between the two characters and their storylines both give off the impression that The Simpsons has replaced Laura Powers with Shauna, whether or not this was intentional on the part of the creators.