Why do you think Frau Hermann allowed Liesel to read books in her library?

Ilsa saw that Liesel loved books enough to put her life in jeopardy by stealing one, and because she has an enormous library wants to share it with the girl. After the book burning, the first time she returns to the Mayor's home, Ilsa beckons Liesel inside. Ilsa brings Liesel into her home library stocked with books. Excited, Liesel runs her hands along the shelves.