It would be complex to state only one main theme, but if you put all the main ideas of the story "Praisesong for the Widow" together, you could argue that the most important one is Culture and Identity. It is culture and identity because the story surrounds the mourning of a widow, who finds solace in re-connecting with her Creole and West Indies/African roots.
It is a metaphor in that the peace came from finding herself and placing herself in charge of her future by recognizing and honoring her past.
"herapplesness" is correct. Some of the main themes of "Praisesong for the Widow" are Culture and Identity, and also add to this journeying - all indicate an attempt by Avey to find meaning in her life, as well as the discovery of her own ancestry.
There are many hints of ancestry that Avey initially doesn't "get,"such as her taking the same route as her slave ancestors did in the Middle Passage: she has been to Ghana, Brazil & the Caribbean, retracing the footsteps, as it were, of her ancestors that were forced against their wills in the Atlantic slave trade.