What do you imagine the mother’s relationship with Dee was like when Dee was at home in the passage?
It is right to commend Dee (Wangero) for embracing her African heritage. However, there is some speculation that she has embraced this heritage because it had become fashionable. Dee has been to college and learned of this heritage and how it is important to reclaim it from an historically repressive white society. This is well and good if she has chosen to embrace this heritage for political and ethical reasons. But most or all of her behavior indicates that her main motivation is to be fashionable. So, it is possible that this new love for African heritage is based on doing what's popular.
The same can be said for her behavior growing up with her mother and sister. In fact, her mother, Mrs. Johnson, says:
Dee wanted nice things. A yellow organdy dress to wear to her graduation from high school; black pumps to match a green suit she'd made from an old suit somebody gave me.
Dee does have ambition. She does read to her mother and sister in order to make them more historically knowledgeable. And she is productive in styling her own clothes. But her interest revolves around fashion and "nice things" as her mother notes. When she returns and asks for the quilts, it is clear she wants to use them as a fashion statement. When she leaves, she tells Maggie to make something of herself and that "it really is a new day for us" (women). This is directed at both her mother and sister. Dee/Wangero has always tried to be a modern woman and it is clearly evident in her parting lines here. Dee was probably focused on the same things while she was growing up: the desire to be modern, fashionable, and in style. This attitude would have clashed with her mother who was and is more traditional and more interested in practical living.