"She teaches nobody."
Translation:Zij onderwijst niemand.
Leren = learning, what the student does.
The teacher teaches, which is onderwijzen, or lesgeven. It can also be leren.
Now, this doesn't always hold up, depending on the object and other verbs present:
- Zij leert hem dansen. -> She teaches him to dance.
- Zij leert dansen -> She learns to dance
- Zij leert hem kennen -> She gets to know him
Zij leert niemand wouldn't really fit in with any of these and wouldn't be a good sentence without another verb at the end. Zij leer niemand dansen would of course be fine, for example.