Campbell has always been thankful for the Scream movies and their importance in her career, but her participation has never been a given. She only returned for Scream 3 after requesting her screentime be cut down, and she had to given convinced to return for both the fourth and fifth movies. Her passing on Scream 6 suggests she might want to permanently move on from the property. The movie's trailer is strongly hinting that Gale Weathers (Courtney Cox) - the other major legacy character - may not survive this next outing either.
With that in mind, Scream 6 could be setting up Kirby as the series' next big legacy survivor. It would feel spiteful for the filmmakers to go to such lengths to confirm Kirby's survival - as her fate was ambiguous following her stabbing in Scream 4 - and to bring her back, only to kill her permanently. Some fan theories suggest she could be Ghostface, but given her experiences, that feels doubtful. If Cox and Campbell are moving on from the movies - which has to happen one day - then Kirby becoming the next recurring survivor is a smart move.