One thing about Yachiru worth remembering is that she is able to sit on Zaraki and be around him even when he's intimidating people with the share force of his reietsu, meaning she most have a considerable amount. Ichigo gets totally mindfucked by his power the first time they meat, that Hanatarou guy passes out and Ganjou can just barely stand it. And having enough reietsu to withstand that must mean that she's actually worthy of the Vice Captain tittle.