If there's a center to the community of black women in the book, it's Ella. She's the one to gather the women together—even the reluctant ones—to exorcise Beloved and save Sethe. All this even though she never agreed with Sethe's killing of baby Beloved (duh) and ignored her after Sethe got out of jail (26.256).
So why does she do what she does?
Well, first, there's Denver, who "[appears] to have some sense after all" (26.256). And Denver's clearly in trouble, too. Ella also has an issue with the past:
Ella didn't like the idea of past errors taking possession of the present […] The future was sunset; the past something to leave behind. And if it didn't stay behind, well, you might have to stomp it out. (26.256)
More specifically? She's totally not cool with idea that Beloved would come back from the dead: "She didn't mind a little communication between the two worlds, but this [Beloved] was an invasion" (26.257).
We're guessing her perspective probably has something to do with her childhood, where "she was shared by father and son […] who gave her a disgust for sex" (26.256). Ella is all about setting and respecting proper limits and boundaries—for good reason.