Mary Wiseman's character, Lt. Sylvia Tilly, was like a breath of fresh air to Star Trek: Discovery. A bubbly, intelligent officer who worked alongside Commander Stamets , Tilly was the first to befriend Michael Burnham when she came aboard Discovery after spending six months in prison for mutiny. That was part of Tilly's nature. She was a friend to everyone aboard the ship, trying to find the good in everyone.
In the fourth episode of the fourth season of Discovery, Tilly left to join Starfleet Academy as one of the instructors. Though she briefly returned to Discovery, she would eventually return to the Academy where she became the longest tenured instructor the Academy had ever had. And that alone is the reason why Wiseman has to be a part of the new series, Starfleet Academy, which is going to be set in the 32nd century.
Unless the series plans on never showing the longest tenured instructor, which doesn't make sense, then Wiseman's character needs to be a part of the series. It would be inconceivable that Tilly would never be seen, unless the cadets aren't going to take any of the classes she teaches. Granted, there may be many different instructors, but would they have more than one teaching the same subject?
Bringing Wiseman to Starfleet Academy is a way to not only tell her story that wasn't really finished on Discovery, but it would also be a link to the 32nd century where we would also, hopefully, see other familiar members of Starfleet. After all, Tilly did tell Captain Burnham that they would see one another around Federation Headquarters.
Starfleet Academy is going to be a show with new characters in a different setting than fans are used to seeing. Having one familiar face would go a long way toward drawing in more viewers, especially if that face is Tilly's. Just by seeing her, we know the show would have heart, humor, and hope!