Ivy is Genevieve's housekeeper who gets her fifteen minutes of fame in the Civil War flashbacks. This lady knows all about resurrecting soldiers, apparently—and she definitely knows it's not a good idea.
Ivy is to Genevieve what Amma is to Ethan. (For all you analogy fans, that's Ivy:Genevieve::Amma:Ethan.) It's pretty appropriate, actually, given that Ivy is an ancestor of Amma. Like Amma, Ivy tends to know what's best. And like Ethan, Genevieve ignores her advice.
This old-time housekeeper doesn't do much other than run around obeying Genevieve's orders. She hasn't yet earned the independence that Amma will enjoy the post-Civil War and post-Civil Rights Movement world.
We do get a glimpse of Ivy one last time, mourning Genevieve's death. In fact, Ivy's the one that buried The Book of Moons with Genevieve's body. Did she think it would never be found, or was she hoping that someone would dig it up someday? Sneaky, Ivy. Very sneaky.