http://fireemblem.wikia.com/wiki/Maribelle
Maribelle is a member of Chrom's Shepherds, and is the daughter of the Duke of Themis, an influential noble family in Ylisse. In her supports with Gaius, it is revealed that in during a period of time preceding the events of Awakening, Gaius once hatched a plan to steal from the Ylissean treasury, but which was foiled when he was captured. Pushing the responsibility of the plot onto Maribelle's father and causing him to be put on trial, Gaius caused Maribelle to develop a deep-seated hatred for him. This hatred is later vanquished when Gaius, albeit reluctantly, admits that he had done so in order to protect her from being targeted by the nobles who had plotted against her father.