Yeah, it's usually the cliche case that a character (Shiina) thinks they're ordinary and not "powerful" when in actuality they have some untouched power hidden within them.
The ending scene is foreshadowing that Shiina had this untapped ability to bring the ~almost dead flower (mimi) back to life. But that's just a theory, a gay theory.
Considering the way the good doctor states: "It's fine. It's fine. My healing magic is irreplaceable" after the spat with the school leadership, followed by her exacerbating the cause of said spat by filling Shiina in completely...
Either the doctor sees her own ability reflected in Shiina, and is grooming her because of that; or, on the slightly darker side, Shiina is being set up to be the next sacrificial lamb to create a new Mimi, or even become the next Mimi herself (we saw that Mimi and she share some odd compatability, as Mimi was able to heal her)...