How does Mrs. Auld “inexperience” with slavery help Douglass ?

Before marrying, Mrs. Auld had no experience with slaves.... she'd never owned one, and she'd never known anyone who had them. When Douglass first meets Mrs. Auld, she is kind, compassionate, and even helpful.... encouraging. It does not take long, however, before she transforms from a kind, sympathetic woman who wanted to teach Douglass how to read, into a vengeful monster.