Clearly, one could argue that Dee/Wangero is trying to reclaim her African heritage. Whereas Mrs. Johnson (narrator) and Maggie live a rural American lifestyle, Dee is attempting to be more African, albeit in a modern African American sense. Dee's fascination with African culture seems more superficial and fashionable than a sincere reclamation of her roots. So, using Dee as one who is trying to undo colonial (in Africa and America) influence is complicated but a worthwhile study.
But, here I would suggest a different and perhaps odd angle. Mrs. Johnson and Maggie are comfortable with their lifestyle. To whatever extent they carry on or celebrate their African heritage, they certainly sustain their more recent, American family traditions (namely, symbolized by the quilts). Note that at the beginning of the story, Mrs. Johnson daydreams about an American Dream moment with Dee. In real life, Mrs. Johnson is big-boned with tough hands and no fashion sense. In the dream, she is how Dee would want her to be: "a hundred pounds lighter, my skin like an uncooked barley pancake. My hair glistens in the hot bright lights." Dee would want her to be a certain way. Dee would want to change her— according to Mrs. Johnson.
Also note how Mrs. Johnson describes the way Dee used to read to her and Maggie:
She use to read to us without pity; forcing words, lies, other folks' habits, whole lives upon us two, sitting trapped and ignorant underneath her voice. She washed us in a river of make-believe, burned us with a lot of knowledge we didn't necessarily need to know.
Dee would force "whole lives upon us two." Dee wanted to change them and their way of life.
However, Mrs. Johnson and Maggie are comfortable with the way they are living. During Dee's visit, they are uncomfortable. Dee arrives and tries to force her modern way of life upon them. To be sure, her interest in African culture and women's empowerment is to be admired. But, the superficiality of her interest aside, she is in fact pushing this new lifestyle upon them in a way that is similar to the act of colonization. I wouldn't go so far as to say that Wangero has returned home to try and colonize her mother and sister. But it is ironic that in trying to reclaim a heritage, she is also trying to erase the more immediate family heritage that her mother and sister still enjoy.
It's a complicated story. Dee's efforts, though they are progressive, are suspect in terms of her sincerity. That notion aside, Walker has put here an interesting and complicated twist. This family can trace their ancestors to (presumably) slaves and eventually Africa itself. But for Mrs. Johnson and Maggie, their meaningful culture is their more recent family history. So, while Dee is discovering her African heritage, it is ironic (or maybe even hypocritical) to try and erase the family heritage of which Maggie and Mrs. Johnson have grown accustomed.