Hortense is Clara Bowden's strict (and strictly religious) mother. If she has a claim to fame, it would be that she was born during a massive and famous earthquake in Kingston, Jamaica. Using her birthing event as supporting evidence, Hortense believes herself to be unstoppable. (Kind of wacky, no?)
Hortense's mother raised her to be deeply religious, and she is deeply involved in the Jehovah's Witness organization. When Clara abandons the church, Hortense wants almost nothing to do with her, although she occasionally tries to remind Clara that when the world ends, only 144,000 believers will ascend to heaven.
On the one hand, Hortense makes it hard to understand how Clara became who she is. The two aren't very much alike. But one of Hortense's biggest roles in this novel is to remind us of how much the past matters. Scenes with Hortense often take us back in time, and through these scenes, we better understand the complications of the present.