Rhiannon was once a queen of some unknown nation.
She went to the White Tower and announced to everyone who she was. She acted very pompous and demanded something unknown from the Aes Sedai. What she received, however, was far from what she wanted.
Centuries after her scene at the White Tower, a tapestry of her being humbled hangs in the corridors. When Elayne Trakand boldly announces who they were to the Kin, Nynaeve al'Meara chides her for it and reminds Elayne of Rhiannon.