I'm trying to complete First Lessons, and what'sherface has asked me to demonstrate that I can cast Fear.

So, I cast fear at a wall. No response.
I cast fear on her. No response.
I charge it all the way and cast it on her. Nothing.

I try to talk to her, and no new dialog options are available. I go through every one and she still just instructs me to cast fear.
What's going on?

If you have a save from before she asks you to show her Fear, load it. There are a couple of things she'll ask you to show her and another may work better. (She asked me for "Heal Other" which worked first try.)

Nevermind, you have to cast it on the emblem nearby.
(edited to fix spelling.)