I found our class discussion on the many meanings of the title of Adichie’s short story Imitation fascinating. One meaning (I can’t remember if this came up in class) is the importance of appearance between Nkem and Amaechi. The first example that comes to my mind is when Amaechi tells Nkem that she should make her husband move his girlfriend out of their home and then let the matter drop (page 34). When Nkem asks Amaechi what her advise would be if her husband was having the affair but not bringing his girlfriend into their home, Amaechi was at a loss for advise. This suggests that upholding the appearance of marital fidelity is more highly valued than actually maintaining this fidelity.
The conversation between the two women also portrays the significance of role of appearance. For example, Amaechi always asks Nkem’s advise on cooking and Nkem always obliges, despite knowing that Amaechi is the more competent cook. Amaechi must know this as well, however, it is understood between them that as mistress of the house, Nkem is expected to be more knowledgeable than Amaechi. Nkem is aware of hypocritical irony of this. She admits her background is far more similar to Amaechi’s than it is to her own husband, but because she married a man of money and status, she is obligated to mirror her husband’s status over those who would have once been considered her social peers. In this sense, imitation becomes a form of deception and money becomes the motivating reason for this deception. Abiding by this standard seems to help both women feel secure and connected to home. Yet, in spite of her self, Nkem feels her ability to maintain this appearance slipping away in America. An example of this is how Amaechi and Nkem confide in one another as sisters, rather than as Mistress and servant. However, Amaechi still has the excuse of appearance to fall back on when a situation gets uncomfortable. For example, when Nkem asks Amaechi to admit that she knows her husband has girlfriends, Amaechi replies: “it is not my place, madam” (page 35).
Nigerian Literature 
You make an interesting connection between Nkem’s assigned role as the wife and Amaechi’s role as the house girl. Nkem obviously feels much closer to Amaechi than is normal or preferable for the woman of the house to feel about her house girl. The roles of wife and house girl, then, seem more like parts to play — imitations of what each woman thinks is the correct way to act according to her specified part — than the way each actually feels or relates towards the other. Part of this is likely derived, as you hint at, from Nkem’s detachment and loneliness from her life in the US. She has nobody to talk or relate to other Amaechi, and yet she still feels the need to play the part of superior because she is a “big man’s wife.”