[X] Write-in: Leave her a note someplace conspicuous (to her) to either obey her commanding officer or hide her involvement better. This half-hearted middle-ground is a bad mix. You'll lecture her later, when it's more convenient.
[X] This is a matter between Wizards, and while you're not of the Jade Order and cannot directly punish her, etiquette dictates that you report this matter to them.
[X] You'd have done the same once. Tell her you understand, but treat her to a lecture on the risks and dangers of miscasts.
-[X] Warn her that you will not be as lenient a second time.
[X] Visit her when she is on her lonesome and ask her how her rest was? Give her a chance to explain herself. Educate her on the topic of how the dwarfs might respond to knowing you have a young-ling Wizard who doesn't understand or respect the chain of command. And that what she does reflects not only on herself, her college and us, but on the Empire and humans as a whole.
-[X] But do praise her initiative. That she could judge how close to the edge she was. She exceeded your expectations. You did not think she had so much mortal and magical endurance. You will certainly take that into consideration for future plans and be sure to assign her more difficult tasks. How did fighting after casting all night and on no sleep go? On that topic, how does she feel about miscasts and was there any trouble during the battle?
[X] While the orc threat seems to be well in hand, you'd feel a lot better if you had more information about the tunnels and the scope of the Skaven threat. And some idea how to deal with a mountain full of trolls.