I agree that the Herdman book is an excellent resource. Who diagnosed her with a vestibular problem? They are not that common in 13 year olds. Cooksey cawthorne exercises are very generic and a bit old but maybe vaguely useful if you are not sure of the problem. the following article gives an overview of a reasonable vestibular examination. As Fisio says, recovery can vary with the pathology. You need to get them to work hard to accomodate or compensate. Knowing the cause would help with prognosis.

http://www.siumed.edu/surgery/clerks...%20Handout.pdf