My thoughts are that he would have included a letter primarily to provide some proof of her version of events as being true, to get her in the door. Secondarily, it would probably say something to the effect of him making his recommendation contingent on her actually arriving successfully. He believes she has the adaptability and perseverance necessary to be a good student, and making such a difficult journey for a tribal Kobold is evidence enough for him. 

If she didn't successfully make the journey, then, well...they'd never get the letter.