If she has dedicated your time to self-education, I cannot imagine she would object to your spending time in the library. Do let me know when your next free afternoon comes around, and I will invite you both to tea; she and I can amuse ourselves, while you explore.

I can think of several people who speak, or read, at least a bit of German, if you would prefer some assistance from a person rather than a translation spell. Professor Sinistra is the one who leaps most quickly to mind; I cannot speak for her, of course, but I do not think she would find a visit from you unwelcome.