Bruh, she has a phone, IN HER HAND. Phone one of the class students and tell them what she just admitted. Tell them what's happened and that she's pinned on the floor. But lemme guess, she's gonna conveniently forget the phone is there until last second and she gets killed before she can. Then, maybe, Oh I don't know. The 1 second phone call will alert immortal dude to come running, he'll arrive, Nana will have already set everything up to look like she wasn't responsible once again.
Then they'll have there usual back and forth of why it could be her, and her defense as to why it isn't. So, then she gets away with it again because he has nothing solid to show the class and maybe a major twist will come at the end of the season were one of them will reveal their powers to be: Bringing talented back to life and healing them completely! Or, sensing murderous intent. Something big and hard to deal with.