In Where is Ce'Nedra's tree?, one of the answers depends on a concept of Ce'Nedra being "half dryad" with other disputing that. This is apparently a common debate in the fandom. The quotes I've found so far don't seem definitive, with the best one from this answer kind of suggesting either direction:
"Ce'Nedra's background makes her peculiarly sensitive to trees," Polgara explained. "I didn't know that Tolnedrans were that interested in the out-of-doors." "She's only half Tolnedran, Liselle. Her love of trees comes from the other side of her heritage." "I'm a Dryad," Ce'Nedra said simply, her eyes still dreamy. - "I didn't know that." "We didn't exactly make an issue of it," Belgarath told her. "We were having trouble enough getting the Alorns to accept a Tolnedran as the Rivan Queen without complicating matters by telling them that she was a nonhuman as well." - King of the Murgos
The Eddings wiki entry on Ce'Nedra states her as being "a dryad" and "a monster" or "non-human", and the entry on Dryads states that the "Dryad trait bred true in Borune females for countless generations".
Now it could be that the confusion is the usual one of race, genetics versus culture and "one-drop" biases where having even some blood from one branch qualifies you as that race, but is Ce'Nedra intended to be a pure-blooded dryad?