Ysalfa

In Karyana's story, there's a minor character named Ysalfa - an elvish merchant. She is met by Laurinya and the others after her cart is attacked by a group of orcs.

Also, Kaina meets a lamia during her travels, after she is knocked off her horse during a chase to escape from a pack of wolves.

This is both. In reality, Ysalfa and the lamia are two of the shape-shifting forms that Leara of Myst took, the last creature form being a dryad.