Why did Miss Rottenmeier stomp out of the room in Heidi?

Dete takes Heidi to be interviewed by Miss Rottenmeier as a possible companion for the invalid Clara. However, the honest and untutored Heidi gives all the wrong answers to her questions, astonishing the woman. For example, Clara admits she is eight, which Miss Rottenmeier thinks is too young a companion for the twelve-year-old Clara. She also likes to be called Heidi, a name Miss Rottenmeier thinks is unchristian. Worst of all, Miss Rottenmeier is horrified to learn that Heidi has never learned to read.
At this point, realizing how badly the interview is going, Dete runs out of the room, planning simply to leave Heidi on Miss Rottenmeier's hands and be done with her. Therefore, Miss Rottenmeier runs out of the room after her in order to get more information before Dete is gone for good:

Fraulein Rottenmeier stood for a moment taken aback and then ran after Dete. If the child was to stop [stay] she had many things yet to say and ask about her, and there the child was, and what was more, Dete, as she plainly saw, meant to leave her there.