I'd say there are two answers here - she must obey her husband's wishes and follow his advice (he tells her not to teach Douglass how to read) and slavery strips her of her innate beliefs and benevolent nature (she used to be a kind and caring person before she got slaves).
This is more like the compass for finding your way out of a geometry book. A mathematical compass (like this one) is used to draw perfect circles. For Donne, it was the perfect metaphor for the long-distance relationship he imagined with his wife. Line 26: The compass is introduced emphasizing two crucial features.
I believe the answer to this is A