She did have a defined role when she was introduced, mainly as a contrast to Burnham and the other half of a mentor-pupil relationship with her. With Burnham off ship, she needed something else to do, and that something is incidentally her speciality. The cast may be small at the moment but I can't make a prediction on the course the show would take with not even Season 1 finished. In the next season she might be commissioned as an Ensign and assigned as a science officer, especially if Burnham becomes first officer, or she might be written out of the show completely to go finish the Academy. That being said, I didn't see her working with Stamets on the spore drive and helping him as disconnected from what was established as her particular field. And we also saw her become more confident, which might not be the most original of character arcs, but it's been way more than Travis Mayweather's weekly mandatory single lines.