Is it the time that Ce'Nedra is trying to get Polgara to complete the story that Belgarath started (in Belgarath the Sorceror), to get the other half of the story (the story of Polgara's life (that becomes Polgara the Sorceress)).
So she and Garion have gone to the cottage in the Vale to visit Durnik, Polgara and the twins. However, Polgara had declined Ce'Nedra's request, refusing to finish the job that Belgarath had left half done.
So later that night Ce'Nedra (whilst they are both in bed) asks Garion to invite Belgarath and Poledra over, so as not to let the opportunity for a visit slip by.
Ce'Nedra believed that Polgara would listen to her mother.