Curious choice. I wonder if they'll bother explaining why we don't see her the subsequent seasons or if they'll lean into the idea that this show is a separate continuity. I don't think they're going to do the latter based on the showrunners' past comments about making sure this show fits in nicely between seasons.
I'm guessing the answer to that is already in the description. Transfer student comes in for one story and then transfers out again when it's over is a pretty common story setup for tv. Especially 'tough kids' who are often portrayed as from families that move around a lot.