Although Alice Walker did not live during the time of slavery - certainly she grew up not far enough removed that she understood the difference between freedom and oppression. As the youngest of 8 children, she grew up in a home that was poor in material wealth, but rich in culture, love, and encouragement. She was always encouraged in her creativity and art even as a child.
Alice Walker's works tend to be woven from the common threads of overcoming oppression, discovering inner beauty and strength, and learning to love yourself and those around you despite adverse circumstances. Clearly she writes a little bit of herself into each of her works - from novels, to poetry to essays, to speeches.
One interesting story about her childhood that she credits as a pin-pointed life shaping moment was the time when one of her older brothers shot her in the eye with a BB gun. Afraid of the consequences for himself, he came up with a story - convinced his little sister to buy into it, and essentially managed to live without guilt over it for the rest of his life. This is the moment that Walker began to understand what betrayal of the truth can do to a person. Harboring this lie - she actually became a victim to the kind of emotional and psychological damage she so beautifully writes for many of her characters.
Add to this her personal experiences with segregation and connection to her obvious heritage of slavery - and you can understand from where she draws the many consistent themes in her work.